Biodegradable copolyester, molded article produced therefrom and process for producing the molded article

ABSTRACT

A biodegradable copolyester having an average molecular weight of at least 50,000 produced by copolymerizing a lactic acid component as the main component with PEG, an aliphatic polyester or a sulfo group-containing ester-forming compound, a molded article produced using it, such as a conjugate fiber, and a process for producing the molded article.

This application is a 371 of PCT/JP94/01489 filed Sep. 8, 1994.

TECHNICAL FIELD

The present invention relates to a novel biodegradable copolyesterhaving a versatility which is applicable to fibers, films, containersand the like and is improved in toughness, degradability, heatresistance and dyeing ability, a molded article having improvedmechanical properties such as toughness produced using the copolyester(for example, polylactic acid fibers having a biodegradability andsuitable for preparing fibrous structures such as a non-woven fabric,conjugate fibers having a controlled biodegradability or ahydrolyzability in neutral environment, conjugate fibers capable ofbeing divided easily even under neutral or weak alkaline environment andcapable of forming into fine fiber, ultrafine fiber or fiber havingspecial section, and fibrous structures prepared using them), and aprocess for producing the molded article.

BACKGROUND ART

Complete circulation type degradable polymers which are finally degradedinto carbon dioxide and water by degradation by means of microorganismsunder natural environment and/or by hydrolysis under neutralenvironment, attract attention recently from the viewpoint ofenvironmental protection.

For example, among such polymers, polyhydroxybutyrate (hereinafterreferred to as "PHB"), polycaprolactone (hereinafter referred to as"PCL") and polylactic acid are known as a melt-moldable andbiodegradable polymer.

However, not only PHB requires a large energy in recovery andpurification of the polymer because of biosynthesis by microorganisms,thus the production cost is too high, but also molding thereof isdifficult because it is difficult to control the molecular weight andthe crystallinity. Also, it is difficult to control the physicalproperties of the molded articles such that the molded articles are poorin transparency. Thus, it is the actual circumstances that it is noteasy to industrially and inexpensively provide performances andmoldability which meet the uses.

Also, PCL has a serious problem and an obstacle in practical use thatthe creep during use is large since its melting point is as low as 60°C. and, therefore, the articles prepared therefrom are poor in shapestability or the strength is extremely lowered depending on the usetemperature.

On the other hand, polylactic acid is relatively inexpensive, and is athermoplastic resin having a sufficient heat resistance since itsmelting point is 178° C. Thus, it is melt-moldable and the use as fibersfor clothing and industrial purposes is expected. Also, although thepolylactic acid is a biodegradable polymer excellent on practical use,it has the problems in production and processing that (1) polylacticacid homopolymer is poor in melt-moldability due to too highcrystallinity, and moreover, the molded articles, films, fibers and thelike obtained therefrom are not sufficient in toughness, and also arefragile and low in impact strength (having a rigid crystal structure),(2) the dye affinity is poor, (3) the molecular weight of polylacticacid cannot be sufficiently raised, (4) if polylactic acid is heated,the molecular weight is decreased, resulting in deterioration ofstrength and the like of the final products, and in addition, atechnique to produce practical fibers for clothing and for industrialuse from polylactic acid has not yet been established, (5) it is behindtechnical development for commercialization as fiber products.

For such a reason, a very limited use such as thread for sutureutilizing the biocompatibility is only hitherto known.

Also, Japanese Patent Publication Kokai No. 1-163135 discloses a drugsustained release base material for releasing drug into living body,which is obtained by reacting a polymer or copolymer of lactic acidhaving a molecular weight of 300 to 10,000 with a polyoxyethylene glycol(hereinafter referred to as "PEG") having a molecular weight of 150 to10,000 in an equivalent ratio of PEG to the polylactic acid of 0.3 to5.0 (30 to 500%).

However, the obtained copolymer is contemplated to use mainly in aliving body. Its softening point (temperature at which stringinessbegins to occur with a glass bar on a hot plate) is as very low as from-10° to 60° C., and the molecular weight is supposed to be at most about10,000 to about 20,000, based on the above-mentioned softening point,ratio of reaction raw materials and state of the product (paste-like orwax-like). Therefore, molded articles excellent in versatility andtoughness cannot possibly be obtained therefrom.

Also, Japanese Patent Publication Kokai No. 63-69825 discloses a blockcopolymer of 70 to 97% (% by weight, hereinafter the same) of polylacticacid segments and 3 to 30% of. polyoxyethylene dicarboxylic acidsegments. It is described therein that the reason why thepolyoxyethylene dicarboxylic acid is used is that if PEG is reacted atthe time of polymerization of a cyclic dimer of lactic acid (hereinafterreferred to as "lactide"), the terminal hydroxyl groups of PEG hindersthe polymerization, so the copolymer having a low degree ofpolymerization is only obtained.

However, the products obtained in the examples of Japanese PatentPublication Kokai No. 63-69825 are only those having a molecular weightof at most 31,000 and a tensile strength of the film of only 2.8 kg/mm²(about 1/10 of the product of the present invention), even ifpolyoxyethylene dicarboxylic acid is used. Further, polyoxyethylenedicarboxylic acid is fairly expensive as compared with PEG and,therefore, the products are not wholly satisfactory also from theviewpoint of versatility.

Besides polymers having biodegradability as mentioned above andartificial fibers prepared therefrom, cotton, wool, silk and the likewhich are natural fibers also have a biodegradability, but there arelimits in strength, fineness, length and the like, so the uses thereofare limited.

Also, in general, if natural fibers are retained in the soil or waterrich in bacteria, the degradation progresses in about 1 to 3 months, andthey have the defect that the article life is too short.

For such a reason, artificial fibers which can be produced to have adesired thickness and length and which have a rate of degradation orrate of deterioration according to necessity, have been stronglydemanded.

Also, conjugate fibers which can be divided by a chemical treatment toproduce, for example, ultrafine fibers, have been widely utilized. Forexample, conjugate fibers that the division is possible by treating withan aqueous solution of a strong alkali (sodium hydroxide and the like)to hydrolyze polyesters, are disclosed in Japanese Patent PublicationKokai No. 57-29610, No. 59-187672 and No. 1-292124. Also, conjugatefibers which can be divided by dissolving and removing a soluble polymer(e.g. polystyrene) with a solvent (hydrocarbon, polar solvent,halogenated compound or the like), are proposed in Japanese PatentPublication Kokai No. 61-282445, etc.

However, these conventional dividable conjugate fibers have manyproblems in safety and environmental protection, since aqueous strongalkali solutions or organic solvents are used in the division.

For example, since alkali hydrolysis uses an aqueous solution of sodiumhydroxide having a high concentration (e.g. 1% or more, especially about3 to about 10%), a large amount of an acid is required in neutralizationof waste water after the hydrolysis treatment. Further, the hydrolysisproducts (sodium terephthalate, etc.) have a low rate of biodegradationand accordingly become a source of environmental pollution. Similarly,in case of using solvents, it is difficult to completely recover thesolvents and the dissolved polymers from the waste water, resulting insource of environmental pollution. Also, if the dangerous aqueous strongalkali solutions or the solvents are used and the treatment of the wastewater thereof is further conducted sufficiently, not only difficultieson working are encountered, but also expensive equipments and highoperating cost are required, thus economically disadvantageous.

It is an object of the present invention to provide a novel polylacticacid copolymer (biodegradable copolyester) which is improved inmoldability and toughness and is improved in rate of degradation, impactstrength and/or dye affinity and moreover has a sufficient heatresistance and which is relatively inexpensive and can be used in a widerange of uses.

A further object of the present invention is to provide molded articlesprepared by melt-molding the above-mentioned polylactic acid copolymer(for example, a melt-adhesive fiber of the polylactic acid copolymerhaving a melt-adhesion property as well as a biodegradability andsuitable for preparing fiber structures having a complete circulationtype biodegradability such as non-woven fabrics and woven and knitfabrics; a novel fiber which is biodegradable or is hydrolyzable under anatural environment, and that it is possible to control its life (periodof use) within a wide range in accordance with necessity and to affordwith a high reliability a very favourable characteristic such thatdeterioration in strength and physical properties is relatively lessduring the use and rapidly proceeds after the life; an improved noveldividable conjugate fiber which can be easily divided under neutral orweak alkaline environment and whose hydrolysis products can be easilydegraded to prevent environmental pollution, and which is low in wasteof resource and is advantageous also in cost and a fiber structureproduced utilizing it).

Another object of the present invention is to provide a novel processfor producing polylactic acid copolymer moldings having a high strengthwhich are improved in formability and toughness and can be used in awide range of uses at low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustrative transverse sectional view of a twin-screwkneading extruder (hereinafter also referred to as "twin-screw kneader")which is a continuous polymerization apparatus suitable for use inpreparing the biodegradable copolyesters of the present invention;

FIG. 2 is an illustrative vertical sectional view of a twin-screwkneader which is a continuous polymerization apparatus suitable for usein preparing the biodegradable copolyesters of the present invention;

FIG. 3 is an illustrative transverse sectional view of a biaxialstirring reactor suitable for use in preparing the biodegradablecopolyesters of the present invention;

FIG. 4 is an illustrative plan view of a biaxial stirring reactorsuitable for use in preparing the biodegradable copolyesters of thepresent invention;

FIG. 5 is an illustrative transverse sectional view of an example of acore/sheath type conjugate fiber which is one of the molded articles ofthe present invention;

FIG. 6 is an illustrative transverse sectional view of a further exampleof a core/sheath type conjugate fiber which is one of the moldedarticles of the present invention;

FIG. 7 is an illustrative transverse sectional view of a still furtherexample of a core/sheath type conjugate fiber which is one of the moldedarticles of the present invention;

FIG. 8 is an illustrative transverse sectional view of another exampleof a core/sheath type conjugate fiber which is one of the moldedarticles of the present invention;

FIG. 9 is an illustrative transverse sectional view of still anotherexample of a core/sheath type conjugate fiber which is one of the moldedarticles of the present invention;

FIG. 10 is an illustrative transverse sectional view of a furtherexample of a core/sheath type conjugate fiber which is one of the moldedarticles of the present invention;

FIG. 11 is an illustrative transverse sectional view of a still furtherexample of a core/sheath type conjugate fiber which is one of the moldedarticles of the present invention;

FIG. 12 is a graph showing an example of a dependency of strengthretention rate on time in a hydrolysis test of a fiber which is themolded article of the present invention and a fiber for comparison;

FIG. 13 is an illustrative transverse sectional view showing an exampleof the transverse sectional structure of a conjugate fiber(half-division conjugate fiber) which is a molded article of the presentinvention;

FIG. 14 is an illustrative transverse sectional view showing an exampleof the transverse sectional structure of a conjugate fiber (radialconjugate fiber) which is a molded article of the present invention;

FIG. 15 is an illustrative transverse sectional view showing anotherexample of the transverse sectional structure of the conjugate fiber(radial conjugate fiber) which is a molded article of the presentinvention;

FIG. 16 is an illustrative transverse sectional view showing stillanother example of the transverse sectional structure of the conjugatefiber (radial conjugate fiber which is a molded article of the presentinvention;

FIG. 17 is an illustrative transverse sectional view showing an exampleof the transverse sectional structure of a conjugate fiber(multifilamentary conjugate fiber) which is a molded article of thepresent invention;

FIG. 18 is an illustrative transverse sectional view showing an exampleof the transverse sectional structure of a conjugate fiber (petal-shapedconjugate fiber) which is a molded article of the present invention;

FIG. 19 is an illustrative transverse sectional view showing an exampleof the transverse sectional structure of a conjugate fiber(multi-islands-sea type conjugate fiber) which is a molded article ofthe present invention;

FIG. 20 is an illustrative transverse sectional view showing aft exampleof the transverse sectional structure of a conjugate fiber (mosaic-likeconjugate fiber) which is a molded article of the present invention;

FIG. 21 is an illustrative transverse sectional view showing an exampleof the transverse sectional structure of a conjugate fiber (multi-layertype fiber) which is a molded article of the present invention;

FIG. 22 is an illustrative transverse sectional view showing an exampleof the transverse sectional structure of a conjugate fiber (specialconjugate fiber) which is a molded article of the present invention;

FIG. 23 is an illustrative transverse sectional view showing an exampleof the transverse sectional structure of a conjugate fiber (hollowradial conjugate fiber) which is a molded article of the presentinvention; and

FIG. 24 is an illustrative transverse sectional view showing an exampleof the transverse sectional structure of a conjugate fiber(core-provided radial conjugate fiber) which is a molded article of thepresent invention;

DISCLOSURE OF THE INVENTION

The present invention relates to a biodegradable copolyester comprisingan L-lactic acid and/or D-lactic acid component as a main component andhaving an average molecular weight of at least 50,000, produced bycopolymerizing said lactic acid component with at least one member of(A) a polyethylene glycol (PEG) having a number average molecular weightof at least 300, (B) an aliphatic polyester and (C) a sulfogroup-containing aromatic compound having two ester-forming groups(hereinafter also referred to as "sulfo group-containing ester-formingcompound").

The present invention also relates to the biodegradable copolyester asdescribed above, where the biodegradable copolyester comprising theL-lactic acid and/or D-lactic acid component as a main component isproduced by copolymerizing with the polyethylene glycol having a numberaverage molecular weight of at least 300 is one produced bycopolymerizing 99.9 to 85% of the L-lactic acid and/or D-lactic acidcomponent and 0.1 to 15 % by weight of the polyethylene glycol having anumber average molecular weight of at least 300, and the melting pointis not less than 110° C.

The present invention also relates to the biodegradable copolyester asdescribed above, where the biodegradable copolyester comprising theL-lactic acid and/or D-lactic acid component as a main component isproduced by copolymerizing with the aliphatic polyester is one producedby copolymerizing 99.5 to 85% by weight of the L-lactic acid and/orD-lactic acid component and 0.5 to 15% of the aliphatic polyester, andthe average molecular weight is not less than 80,000 and the meltingpoint is not less than 110° C.

The present invention also relates to the biodegradable copolyester asdescribed above, where the biodegradable copolyester comprising theL-lactic acid and/or D-lactic acid component as a main component isproduced by copolymerizing with the sulfo group-containing aromaticcompound having two ester-forming groups is one produced bycopolymerizing 99.5 to 80% by weight of the L-lactic acid and/orD-lactic acid component and 0.5 to 20% of the sulfo group-containingaromatic compound having two ester-forming groups.

The present invention further relates to a molded article obtained bymelt-forming a biodegradable copolyester comprising an L-lactic acidand/or D-lactic acid component as a main component and having an averagemolecular weight of at least 50,000, said copolyester being produced bycopolymerizing said lactic acid component with at least one member of(A) a polyethylene glycol having a number average molecular weight of atleast 300, (B) an aliphatic polyester and (C) a sulfo group-containingaromatic compound having two ester-forming groups.

The present invention also relates to the molded article as describedabove, where the molded article produced by melt-formation is aconjugate fiber comprising (a) a biodegradable copolyester having amelting point Ta and (b) a biodegradable copolyester which has a meltingpoint lower than Ta by at least 10° C. or which is amorphous and has nomelting point.

The present invention also relates to the molded article as describedabove, where the molded article produced by melt-forming is composed ofa sheath made of a less degradable copolyester that the rate ofdegradation by biodegradation or by hydrolysis in neutral water oraqueous solution is low, and a core made of a biodegradable copolyesterhaving a rate of degradation of at least 2 times the rate of degradationof said sheath, and both said core and sheath components aremolecular-orientated.

The present invention also relates to the molded article as describedabove, where the molded article produced by melt-forming is a dividableconjugate fiber made of said biodegradable copolyester and afiber-forming copolyester containing at least 40% by weight of acomponent derived from an aromatic compound, wherein said fiber-formingcopolyester is divided by said biodegradable copolyester into aplurality of segments in the transverse section of the single fiber andsaid biodegradable copolyester occupies at least a part of the fibersurface.

The present invention still further relates to biodegradable copolyestercomprising an L-lactic acid, D-lactic acid and/or their cyclic dimer(lactide) component as a main component, which comprises continuouslypolymerizing in the molten state a mixture containing said lactic acidcomponent and at least one member of (A) a polyethylene glycol having anumber average molecular weight of at least 300, (B) an aliphaticpolyester and (C) a sulfo group-containing aromatic compound having twoester-forming groups to produce the biodegradable copolyester having anaverage molecular weight of at least 50,000, introducing the copolyesterdirectly to a molding machine without solidification and pelletization,and melt-forming it.

The present invention also relates to the process described above, where99.5 to 85% by weight of L-lactic acid, D-lactic acid and/or a cyclicdimer thereof (lactide) and 0.1 to 15% of by weight of polyethyleneglycol having a number average molecular weight of at least 300 arecontinuously copolymerized in a molten state, and the obtainedbiodegradable copolyester having an average molecular weight of at least70,000 is directly led to a spinning head without solidification andpelletization, and is subjected to melt-spinning, drawing at least 3times and heat-treatment to impart a fiber strength of at least 3 g/dwith maintaining an average molecular weight of at least 70,000.

The biodegradable copolyester of the present invention is, as mentionedabove, a biodegradable copolyester comprising an L-lactic acid and/orD-lactic acid component as a main component and having an averagemolecular weight of at least 50,000, produced by copolymerizing thelactic acid component with at least one member of (A) a polyethyleneglycol having a number average molecular weight of at least 300, (B) analiphatic polyester and (C) a sulfo group-containing ester-formingcompound.

The average molecular weight in the biodegradable copolyester of thepresent invention means a weight average molecular weight of highmolecular weight compounds (excepting those having a molecular weight ofnot more than 500) by GPC analysis (by calibration based on standardpolystyrene samples) of a 0.1% chloroform solution of the copolyester.

The above-mentioned L-lactic acid and/or D-lactic acid component(hereinafter also referred to as "lactic acid component") is a componentto impart good biodegradability and hydrolyzability and also to imparttoughness, heat resistance and crystallinity to the biodegradablecopolyester of the present invention.

The polyethylene glycol having a number average molecular weight of atleast 300 used as the component (A) to form the copolyester with thelactic acid component is a component to impart good formability (drawingproperty, spinning property), impact resistance and hydrophilic propertyto the biodegradable copolyester of the present invention. The aliphaticpolyester (B) is a component which serves to impart a good formability(drawing property, spinning property) to the biodegradable copolyesterof the present invention with control in biodegradation rate andcrystallinity (degree of crystallization) and improvement in thermalcharacteristics of the copolyester. The sulfo group-containingester-forming compound (C) is a component used to impart a hydrophilicproperty and to control the biodegradation rate while improving the dyeaffinity of the biodegradable copolyester of the present invention so asto be dyeable with cationic dyes.

The biodegradable copolyesters of the present invention are products ofcopolymerization of the lactic acid component with one of the components(A) to (C), or with two or more of the components (A) to (C), namely thecomponents (A) and (B), the components (A) and (C), the components (B)and (C) or the components (A), (B) and (C), and the main component ofthe copolyester is the lactic acid component.

That the main component is the lactic acid component means that thebiodegradable copolyester of the present invention contains at least80%, especially at least 85%, further especially at least 90%, of thelactic acid component, more especially from not less than 92% to notmore than 99.9%, especially not more than 99%, more especially not morethan 98%, of the lactic acid component. As a result, there are obtainedthe effects that the biodegradability, toughness, heat resistance andbiocompatibility become good.

From the viewpoints of good formability (spinning property, injectionmoldability) and good biodegradability, it is preferable that theaverage molecular weight of the copolyester is not less than 50,000,especially not less than 80,000, more especially not less than 100,000,and is at most 500,000, especially at most 250,000.

The biodegradability of the biodegradable copolyester can be evaluatedby observing the weight, strength, shape and molecular weight of samplesin the form of fiber, film or plate placed in water, soil or activatedsludge with the lapse of time. For example, the biodegradability may beevaluated good if the tensile strength is decreased to not more than1/2, preferably not more than 1/3, more preferably not more than 1/4,when the fiber is immersed in an activated sludge (ASTM D 5271-93) for 6months.

Like this, since the biodegradable copolyesters of the present inventionare those produced by copolymerizing the lactic acid as a main componentwith the components (A) to (C), preferably by block-copolymerizing them,the impact resistance, formability, heat stability and dyeing propertyand the like of polylactic acid are improved with keeping the propertiesof the polylactic acid such as high melting point and high strength.

Copolyesters of the lactic acid component and the component (A)(hereinafter also referred to as "copolyester (A)") will be explainedbelow.

With respect to the copolymerization proportions of the lactic acidcomponent and the component (A) in the copolyester (A), the proportionof the component (A) in the copolyester (A) is from 0.1 to 15% byweight, preferably 0.3 to 10% by weight, more preferably 0.5 to 8% byweight. There is a tendency that the higher the proportion of thecomponent (A), the softer the copolyester becomes, and the melting pointis lowered and the degree of polymerization is hard to rise. The higherthe molecular weight of the component (A), the less the degrees of thelowering in degree of polymerization and melting point. Therefore, incase of using the component (A) having a low molecular weight, it is notdesirable to increase the copolymerization proportion too much. Forexample, it is preferable that the proportion of the component (A) isfrom 0.3 to 3.9% in case of the component (A) having a number averagemolecular weight of 1,000, from 0.3 to 6.8% in case of the component (A)having a number average molecular weight of 3,000, from 0.3 to 9.4% incase of the component (A) having a number average molecular weight of6,000, and from 0.3 to 12% in case of the component (A) having a numberaverage molecular weight of 10,000.

The present inventors have found experimentally that there is arelationship of equation (III) between the number average molecularweight (x) of the component (A) and the preferable copolymerizationproportion (y) thereof.

    0.3≦y(%)≦[(x-300)/8×10.sup.5 ].sup. 1/2 ×100+1(III)

There is a tendency that the higher the copolymerization proportion ofthe component (A), the larger the hydrophilic property, rate of alkalihydrolysis and rate of biodegradation of the copolyester (A) become, andthe elasticity such as Young's modulus and the heat resistance such asmelting point of the copolyester (A) are lowered as compared with thelactic acid homopolymer. It is preferable to select the molecular weightand copolymerization proportion of the component (A) in accordance withthe purpose of the use.

Also, with respect to the molecular weight of the copolyester (A), theaverage molecular weight is at least 50,000 from the viewpoint that themolded articles thereof (including films and fibers) are excellent intoughness, and is preferably at least 60,000, more preferably from80,000 to 300,000. The fluidity at the time of melting and theformability are inferior if the molecular weight is excessively high,and from such a point of view the average molecular weight is at most500,000, preferably not more than 400,000, more preferably not more than300,000.

Further, with respect to the manner of binding between the lactic acidcomponent and the component (A) in the copolyester (A), they are boundbasically in such a manner that a carboxyl group in the lactic acidcomponent is condensed to a terminal hydroxyl group of the component(A), and a carboxyl group of another lactic acid is condensed to thehydroxyl group of the condensed lactic acid component. Further,optionally used third components mentioned after bind thereto as a chainextending agent, or as a group for controlling biodegradation, a groupfor forming a microdomain structure, a group for improving the dyeingproperty, a group for imparting a hydrophilic property, or the like.

Such copolyesters (A) have a melting point of not less than 110° C. Thehigher the melting point, the more preferable from the viewpoint of heatresistance. For example, molded articles such as food containers arerequired to be able to make a sterilization treatment with boiling waterof 100° C., and for meeting this requirement it is necessary that themelting point is not less than 110° C., and it is particularly preferredthat the melting point is not less than 130° C. Similarly, in case ofusing as a fiber too, it is required to withstand dyeing andsterilization at 100° C., and for meeting this requirement it isnecessary that the melting point is not less than 110° C., and it isparticularly preferred that the melting point is not less than 130° C.Further, it is desirable to withstand severe sterilization (highpressure steam of 130° C.) and high pressure dyeing (high pressure waterbath of 130° C.), and to meet this requirement it is preferable that themelting point is not less than 150° C.

Explanation is given below with respect to the lactic acid and thecomponent (A) constituting the copolyester (A).

The lactic acid component may be included in any form of polymer unitsof L-lactic acid and/or D-lactic acid and/or their cyclic dimers(lactide), that is to say, a unit of poly(L-lactic acid) (hereinafteralso referred to as "PLLA"), a unit of poly(D-lactic acid) (hereinafteralso referred to as "PDLA") and a unit of copolymer of L-lactic acid andD-lactic acid (hereinafter also referred to as "PL/DLA"). It ispreferable that PLLA or PDLA homopolymer units are formed.

In case of forming PL/DLA units, it is preferable to form the unitswherein a slight amount, e.g. not more than 5%, preferably not more than2%, more preferably not more than 1%, of an optical isomer iscopolymerized. Although PLLA and PDLA are both preferably used for thepurpose of the present invention, it is efficient to prepare L-lacticacid (low cost) rather than the other when the raw material lactic acidis prepared by a fermentation method. Therefore, PLLA or copolymerscontaining it as a main component are preferable. If the optical isomeris copolymerized in an amount exceeding 5 degrees of lowering incrystallinity, heat resistance and strength of polylactic acid becomelarge.

Although PEG which is the component (A) constituting the copolyester (A)is a polymer of ethylene oxide, the PEG comprehends those containing astarting material to which ethylene oxide is addition-reacted, whereinethylene oxide is added to the starting material, e.g., water orethylene glycol, bisphenol A, an alkylamine having a C₁ to C₂₀ alkylgroup, or a tri- or more valent compound such as glycerol,trimethylolpropane, pentaerythritol, sorbitol or castor oil. As thecomponent (A), there can also be used polymers prepared by addition ofethylene oxide to an aliphatic polyester wherein a polymer of a hydroxyacid such as lactic acid, glycolic acid, hydroxycaproic acid,hydroxyvaleric acid or hydroxybutyric acid is introduced into theabove-mentioned tri- or more valent compound.

For instance, in case of containing PEG having a branch, the impactresistance and the heat resistance are improved.

The component (A) is required to have a molecular weight of not lessthan 300 in terms of number average molecular weight. In order to obtainthe copolyester (A) having a high degree of polymerization and a highmelting point, the higher the molecular weight of the component (A), thebetter. Preferably, the molecular weight is at least 1,000, especially3,000, further from 5,000 to 30,000, especially from 8,000 to 30,000.

The copolyester (A) may contain a third component by copolymerizing thelactic acid component as the main component and the component (A) withthe third component. Examples of the third component are, for instance,a dicarboxylic acid component used for example to balance the hydroxylgroup of the component (A), a sulfo group-containing compound used forexample to improve the dyeing property (for example, it is possible tomake dyeable with a basic dye by copolymerization with sulfoisophthalateor its metal salt), a compound having amino or amido group (for example,it is possible to make dyeable with an acid dye by copolymerization withan amino acid), and the like.

With respect to the above-mentioned balancing the hydroxyl group of thecomponent (A), both ends of the lactic acid component are carboxyl groupand hydroxyl group, and addition of the component (A), which hashydroxyl groups at both ends (PEG), to the lactic acid component resultsin presence of excess hydroxyl group, and the reaction stops when allcarboxyl groups have reacted. The larger the amount of PEG added, andthe smaller the molecular weight of PEG, the more the balance in molarratio between carboxyl group and hydroxyl group is lost, thus onlyproducts having a low degree of polymerization are obtained. Thisunbalance can be eliminated by adding a substantially equimolar amountof the dicarboxylic acid component based on the hydroxyl group of PEG tothe polymerization system.

The above-mentioned substantially equimolar amount means that the ratioof the dicarboxylic acid component to the component (A) is from 0.8 to1.2 by equivalent (substantially by mole), preferably 0.9 to 1.1 byequivalent. Of course, even if the equivalent ratio is less than 0.8 orexceeds 1.2, effects are obtained in its own way and products having ahigher degree of polymerization are obtained as compared with no use.

Examples of the dicarboxylic acid component utilizable are, forinstance, an aliphatic dicarboxylic acid having about 4 to about 12carbon atoms such as adipic acid, sebacic acid or decanedicarboxylicacid; an aromatic dicarboxylic acid having 8 to 20 carbon atoms such asisophthalic acid, terephthalic acid or naphthalene dicarboxylic acid;their acid hydrides; their esters with a low molecular weight alcoholhaving 1 to 6 carbon atoms such as their methanol ester or theirethylene glycol ester; a dicarboxylic acid halide such as phthaloyldichloride; and the like.

With respect to a manner of the copolymerization of the dicarboxylicacid component, for example, the molecular weight may be effectivelyincreased by adding and mixing a substantially equimolar amount ofphthalic anhydride at the stage that the polymerization proceeds to someextent (middle stage or final stage) to cause it to react with hydroxylgroups each present at the molecular chain end of each of two molecules.For example, adipic acid has a molecular weight of 146 and, therefore, abalance is obtained by addition thereof in an amount of about 1% withrespect to PEG having a number average molecular weight of 15,000. Incase that the lactic acid component is copolymerized with 3% of PEGhaving a number average molecular weight of 15,000, only 0.03%, based onthe whole, of adipic acid as a balancing agent is sufficient. However,if PEG having a number average molecular weight of 300 is used, it isnecessary for balancing to use adipic acid in an amount of about halfthe PEG.

PEG and the dicarboxylic acid component may be added separately to thereaction system as mentioned above, or they may be previously reacted(polymerized) to produce a polyetherester which is then reacted withlactic acid, lactide and/or polylactic acid. The latter is also aneffective method for adding the dicarboxylic acid component to thepolymerization system and reacting it. Similarly, utilizable arepolyester oligomers having many carboxyl groups obtained by reacting anexcess amount of the dicarboxylic acid component with a diol component,for example, an oligomer of hexamethylene adipate prepared in a molarratio of hexanediol/adipic acid of 1/2, 2/3, 3/4 or the like.

Since these third components to be copolymerized tend to lower themelting point of the obtained copolyester (A), the amount thereof isrequired to be within the range capable of maintaining the melting pointwithin the predetermined range. It is desirable that the proportion ofthe third component in the copolyester (A) is usually not more than 2%,especially not more than 1%.

Next, an explanation is given below with respect to a process for thepreparation of the copolyester (A).

The copolyester (A) is prepared by, using for example a twin-screwkneading extruder equipped with a vent or a similar apparatus havingagitation and delivery functions, reacting the raw material and thepolymer in the molten state with agitating, mixing, transferring anddegassing, and then continuously taking out.

By preparing the copolyester (A) in such a manner, it is possible toprepare the copolyester (A) having a high degree of polymerization withless decomposition products and less discoloration in a short period oftime as compared with a conventional batchwise process.

The twin-screw kneading extruder (twin-screw kneader) includes axesarranged in parallel and rotatable in the same direction or counterdirection, which are provided with screws engaged with each other(sending part) and a plurality of two blade-shaped or three blade-shapedagitating elements (many agitating elements) engaged in the same manner.Further, the cylinder (cylindrical part) may be provided, as occasiondemands, with a single or a plurality of vent holes for feeding the rawmaterials or additives or for exhaust in a reaction under reducedpressure.

The polymerization raw materials or the polymer during or after thepolymerization is very efficiently agitated, mixed and transferred bythe twin-screw kneader to fairly accelerate the rate of reaction.Moreover, dead space where the polymer stagnates or sticks, is scarcelyseen.

The agitating elements and screw of one axis are engaged with those ofanother axis, whereby the polymer or the like is always scraped offmutually (self-cleaning action).

Similarly, the polymer or the like is always scraped off from the innersurface of the cylinder by the agitating elements and the screws,thereby preventing them from sticking thereto for a long time.

Consequently, less-deteriorated, uniform and excellent polymers areobtained.

FIG. 1 shows an instance of an illustrative transverse sectional view ofthe twin-screw kneader.

In FIG. 1, two blade-shaped (elliptic) agitating elements 3 and 4 whichare rotatable in the same or counter direction by two driving shafts 1and 2, scrape off the reaction product sticking to the surfaces thereofwith each other or the reaction product sticking to the inner surface ofcylinder 5, thus preventing the polymer or the like from staying at acertain place. Simultaneously, its excellent agitating abilityaccelerates the rate of reaction of the reaction product travellingthrough space 6 and raises remarkably the uniformity thereof. Numeral 7is a heating block, and paths 8 for heat medium are provided thereinwhereby the cylinder 5 is heated or cooled as occasion demands. Theheating of the cylinder 5 may be conducted by electric heating insteadof heat medium, and the cooling may be air cooling. Numeral d in thefigure shows the inner diameter of the cylinder 5.

FIG. 2 is an illustrative vertical section view of the twin-screwkneader (provided that a kneading device is shown as an illustrativeside view).

In the figure, mutually engaging screws are provided on the drivingshafts to form liquid-sending part 10, and similarly mutually engagingagitation elements are provided to form kneading part 11. The rawmaterials fed from feed part 9 are heated and mixed in threeliquid-sending parts and three kneading parts, thus transferring in thecylinder with undergoing reaction, and sent out of output port 14.Cylinder 5 is provided with two vents 12 and 13, whereby it is possibleto conduct feeding of inert gas, exhaust, pressure reduction by vacuumpump, supplemental feeding of raw material, feeding of additive, and thelike. Single screw extruders can be used in the continuouspolymerization for preparing the copolyester (A) of the presentinvention, but twin-screw extruders having excellent features asmentioned above are more preferred. Numeral 15 in the figure is adriving part.

In addition to the above-mentioned kneader-type polymerizationapparatus, a horizontal type or vertical type tank-like reactor having acircular, elliptic or similar shaped section wherein a multiplicity ofdisk-like or similar agitation elements are arranged on two rotationaxes so as to overlap with each other, can also be used in thepreparation (continuous polymerization) of the copolyester (A), sincedead space is a few, it has a self-cleaning action and pressurereduction is possible.

FIG. 3 shows an example of an illustrative transverse section view of aninstance of the reactor equipped with biaxial agitator.

In FIG. 3, reaction product 21 is agitated and mixed by rotating plates18 and 19 attached to two driving shafts 16 and 17, and is passed, withthe reaction product and polymer adhering to the rotating plates 18 and19, through space 22 during which reaction products having a low boilingpoint (water, alcohol, etc.) and the residual monomer are evaporated anddischarged from exhaust hole to the outside of the system.

In FIG. 3, numeral 20 is a reactor, and numeral 23 is an exhaust hole.

The features of the reactor of this type are that the evaporation areafor reaction products can be made large and the increase in capacity iseasy. The rotating plates may have flat surface, or may be provided withunevenness or projections, or may be in the multi-blade shape or screwshape.

FIG. 4 is an illustrative plan view of the above reactor. It would beclearly understood from the figure that a multiplicity of the rotatingplates 18 and 19 attached to two driving shafts 16 and 17 are arrangedin a mutually overlapping relation. The reaction products and thepolymer are fed from inlet 24 on the right side by a liquid-sending pumpor the like and sent out from outlet 25 on the left side by a pump orthe like as needed. It is easy to control the feed amount by a signal ofa level gauge in order to keep the liquid level constant.

The reactor 20 shown in FIG. 4 is of a horizontal type wherein thedriving shaft is horizontally disposed, and the reaction products in thereactor transfer from the inlet 24 toward the outlet 25 by gravity orthe like. A vertical type reactor wherein the driving shaft isvertically disposed, has the same agitating effect, but it is difficultto increase the evaporation area.

The rotating directions of the shafts of the biaxial kneader and thereactor equipped with biaxial agitator may be the same direction or thecounter direction, but the rotation in the same direction is large inthe agitation effect and the shearing force. In FIG. 3, there is shownan instance wherein the clearance between the rotating plates 18 and 19and the reactor 20 is somewhat large, but it is possible to make thisclearance narrow, to provide a constricted part in the center part ofthe section like FIG. 1, to make an upper space 22 large, to provide ahole for feeding additives, to conduct heating of reactor 20 by electricheating or heat medium, and to make various other applications.

In the preparation (continuous polymerization) of the copolyester (A), aplurality of the single screw extruder, the twin-screw kneader and thebiaxial agitating type reactor can also be used in a manner of combiningin multistage. For instance, a first twin-screw kneader can be used forconducting the melting, mixing, dehydration and initial polymerizationof powdery or flake-like raw materials for polymerization (lactic acid,lactide, PEG, antioxidant, catalyst, additives and the like), and forthe polymerization in the middle and final stages, second and thirdtwin-screw kneaders or biaxial agitation type reactors connected theretocan be used for the polymerization in the middle and final stages, and asingle screw extruder can be used in part.

The raw materials for polymerization can be previously, separatelymolten and fed to a polymerization apparatus respectively by measuringpumps.

In the above-mentioned continuous polymerization process, thepolymerization is completed in less than 1 hour, especially 50 minutes,more especially 10 to 30 minutes, so the deterioration of the polymercan be minimized. Comparing with the before-mentioned Japanese PatentPublication Kokai No. 1-163135 wherein it is described that thepolymerization time is from 1 to 10 hours and it takes a long time suchas 215° C.×5 hours in Example 1, 195° C.×8 hours in Example 2 and 210°C.×6 hours in Example 3, it is understood that the polymerization timeis very short. In particular, when the polymerization is carried outunder a reduced pressure, the reaction rate can be further accelerated.

When a solvent is used, polymerization at low temperatures is possiblewhereby the polymer is prevented from deteriorating, but in industrialaspect it is disadvantageous in cost and safety.

Further, by copolymerizing PEG which is the component (A) in an amountof 0.1 to 15%, preferably 0.3 to 10%, the most preferably 0.5 to 8%, theobtained copolyester is remarkably improved in heat fluidity, so thepolymerization procedures, particularly mixing, degassing and liquidsending, are become easy and the copolyester having uniformity andexcellent quality is obtained. Also, the obtained copolyester isexcellent in strength, whiteness, spinning property and drawingproperty.

It is preferable to use an antioxidant upon the preparation of thecopolyester (A).

Since the PEG (A) is a chemically unstable compound easy to be oxidized,it is partially decomposed, so the product having a high degree ofpolymerization is hard to obtain, if the melt-copolymerization iscarried out for a long time without using an antioxidant (in case ofusing no antioxidant, PEG is decomposed during the polymerization togenerate aldehyde or the like). The decomposition can be prevented byadding about 10 to about 3,000 ppm, preferably 50 to 1,000 ppm, of anantioxidant to the polymerization system. The use of a too large amountof the antioxidant may hinder the polymerization, and at the time ofpolymerization it is desirable to use it in a necessary and minimumamount.

However, in order to raise the stability of the obtained articles, anantioxidant may be added and mixed in an amount of about 0.1 to about 3%at the time when the copolymerization has proceeded.

Hindered phenols, hindered amines and other known antioxidants are usedas the antioxidant to be used during or after the polymerization. Theaddition rate is preferably from about 10 to about 30,000 ppm,especially 50 to 10,000 ppm.

Examples of the antioxidant are hindered phenols such as "Irganox"series antioxidants made by Ciba Geigy Corp., and hindered amines suchas "Tinuvin" series antioxidants made by Ciba Geigy Corp., and examplesof the ultraviolet absorber are benzotriazole compounds such as"Tinuvin" series ultraviolet absorbers made by Ciba Geigy Corp., and"Irgaphos" series ultraviolet absorbers which are mixtures of thebenzotriazole ultraviolet absorbers with phosphite stabilizers.Similarly, "Sumilizer" series antioxidants which are phenol antioxidantsmade by Sumitomo Chemical Company, Limited, and "Sumisorb" which is alight stabilizer made by Sumitomo Chemical Company, Limited are alsomentioned. As the antioxidants other than the above-mentioned, there canalso be used thioether antioxidants and the like. Further, there aremany cases that combination use of two or more of the above-mentionedstabilizers is preferable. Further, compounds having a large molecularweight, thus having a high boiling point or sublimation point, arepreferred from the viewpoint of heat resistance. For example, withrespect to the molecular weight, those having a molecular weight of notless than 500, especially not less than 700, are preferred. Irganox 1010(molecular weight 1178) mentioned above is the most preferable example.Also, as the antioxidant and ultraviolet absorber there are preferredsafe ones having no toxicity and no skin irritation.

Catalysts for polymerization reaction can be used upon preparing thecopolyester (A).

As the catalysts, there can be used catalysts used for thepolymerization of lactic acid and lactide, and catalysts used for thepolymerization of polyesters. For example, as transesterificationcatalysts among the polymerization catalysts for polyesters, there arementioned alcoholates of various alcohols with Na and Mg, carboxylates,carbonates, sulfonates and phosphates of Zn, Cd, Mn, Co, Ca, Ba, Sn andso on, oxides, hydroxides and halides of Mg, Pb, Zn, Sb, Ge and so on,and the like.

Upon selecting the catalyst, it is preferable to give consideration todiscoloration of the product, side reaction or no formation ofaggregated foreign matter, to say nothing of catalytic function.

The amount of the catalyst is usually from 10⁻³ to 10⁻⁶ mole/mole basedon the amount of ester, and it is preferable to suitably select inaccordance with the temperature and the reaction system.

With respect to the polymerization catalysts for polyesters, usualcatalysts such as antimony trioxide and germanium oxide can be used.Also, in case of the reaction to obtain a lactide from lactic acid, zincoxide, antimony trioxide and the like are well known, and in case of thepolymerization reaction of the lactide, tetraphenyltin, stannouschloride, diethylzinc, tin octylate and the like are well known.

Of course, other catalysts than the above-mentioned can be utilized ifthey are excellent ones which are large in rate of reaction and causeless discoloration and side reaction.

In general, in case of subjecting the lactic acid component to amelt-polymerization, a part of the lactic acid component (such as lacticacid and lactide) tends to remain in the polymerization system in theunreacted state. If the remaining lactic acid component or a lowmolecular weight oligomer is present in the final products (such asmolded articles, films, fibers, etc.), it serves as a sort ofplasticizer, thus may bring about favorable things such as imparting asoftness to the products. However, if the remaining low molecular weightcompounds are present in excess, it may impair the quality of theproducts or may ooze out during the preparation steps or during the useto contribute troubles. For this reason, the amount of low molecularweight compounds (compounds having a molecular weight of not more than500) remaining at the time of finishing the polymerization is preferablyat most 20%, especially at most 10%, more especially at most 7%, furthermore especially at most 5%, the most especially at most 3%. Fordecreasing the remaining lactic acid component and low molecular weightcompounds, it is also effective to remove them by raising the degree ofvacuum in the middle to final stage of the polymerization, or to add andmix a polymerization initiator (alcohols such as ethylene glycol,glycerol, propylene glycol, PEG and polypropylene glycol also serve asthe initiator) or a polymerization catalyst.

The polymer after the completion of the polymerization can be directlyand immediately subjected to spinning or film formation, or can also beformed into molded articles, films or sheets, fibers and the like afteronce pelletizing it.

The spinning can be conducted by known methods such as melt spinningmethod, dry spinning method, wet spinning method, dry-wet spinningmethod and the like. Drawing, heat treatment, crimping and the like canalso be carried out, as occasion demands. In particular, the meltspinning is preferable since it can be conducted at a high rate in ahigh efficiency.

In case of preparing films or the like, the film is formed by a meltextruding method, and it is subjected to stretching and heat treatmentif needed.

Also, in case of preparing various molded articles, the molding can beconducted by melt extrusion, injection molding and the like.

The films prepared from the copolyester (A) show preferably a tensilestrength of at least 20 kg/mm², and the fibers prepared from thecopolyester (A) show preferably a tensile strength of at least 2 g/d.

The copolyester (A) of the present invention has a markedly excellentmelt fluidity as compared with the homopolymers such as PLLA, and isexcellent in applicability to partly oriented yarns (POY) prepared byhigh speed spinning at a spinning rate of at least 3,000 m/min., highlyorientated yarns (HOY) prepared at a spinning rate of at least 4,000m/min., spin-draw method (SPD) wherein the spinning and the drawing arecontinuously carried out, and step for Spun Bond non-woven fabricwherein spinning and forming into non-woven fabric are conductedsimultaneously or subsequently. The copolyester (A) is greatly differentin that a conventional PLLA homopolymer is remarkably inferior inapplicability these high to efficient spinning methods. Similarly, thecopolyester (A) of the present invention is also far superior to theconventional homopolymer in injection moldability to various containersand various parts, and film forming property and stretchability in thepreparation of films.

Next, an explanation is given below with respect to copolyesters of thelactic acid component and the component (B) (hereinafter also referredto as "copolyester (B)").

With respect to the proportions of the lactic acid component and thecomponent (B) in the copolyester (B), the proportion of the component(B) in the copolyester (B) is from 0.5 to 15% by weight, preferably 1.0to 10% by weight. The higher the content of the component (B) (aiiphaticpolyester), the copolyester tends to become softer and to have a lowermelting point. Therefore, it is not preferable to increase the contentof the component (B) to too high level. For example, preferably thecontent of the component (B) is from 0.5 to 60% when the component (B)has a weight average molecular weight of 1,000, from 0.5 to 10.0% whenthe component (B) has a weight average molecular weight of 3,000, andfrom 0.5 to 12% when the component (B) has a weight average molecularweight of 6,000.

Since the copolyester (B) alters its hydrophilic property, rate ofalkali hydrolysis, rate of biodegradation, elasticity such as Young'smodulus and heat resistance such as melting point depending on theproportion of the component (B), as compared with polylactic acidhomopolymer, it is preferable to select adequate molecular weight andproportion of the component (B) to be copolymerized.

Two or more of the component (B) having different molecular weights canbe used in combination. In that case, like the case of the component(A), the average molecular weight of them is adopted as the molecularweight.

Also, from the viewpoint of excellent toughness of the molded articles(including films and fibers), it is preferable that the copolyester (B)has an average molecular weight of at least 50,000, especially at least60,000, more especially from 80,000 to 300,000. Since the fluidity atthe time of melting and the formability are poor if the averagemolecular weight is excessively large, the molecular weight (molecularweight calculated based on polystyrene by GPC measurement) is, from suchpoints of view, at most 500,000, preferably not more than 300,000, morepreferably 100,000 to 200,000.

Further, with respect to the manner of binding between the lactic acidcomponent and the component (B) in the copolyester (B), in case that theboth ends of the component (B) are hydroxyl groups or carboxyl groups,they are bonded in a manner like in the case of the copolyester (A) suchthat a group, e.g. carboxyl group, in the lactic acid component iscondensed to a terminal group, e.g. hydroxyl group, of the component(B), and the lactic acid is successively condensed. Therefore, in thatcase, it is preferable for obtaining a high molecular weight to use adicarboxylic acid component or a diol component as a third componentlike in the case of the copolyester (A).

On the other hand, in case that one terminal group of the component (B)is hydroxyl group and the other terminal group is carboxyl group, itreacts in the same manner as the lactic acid component and, therefore,random copolymer type or block copolymer type copolyesters (B) areobtained depending on how to react. In this case, a high molecularweight is obtained even if a dicarboxylic acid or diol component is notused.

Such copolyesters (B) have a melting point of at least 110° C. Thehigher the melting point, the more preferable for the same reason as inthe case of the copolyester (A).

Next, an explanation is given below with respect to the component (B)constituting the copolyester (B). The explanation concerning the lacticacid component is omitted because of being the same as the case of thecopolyester (A).

An aliphatic polyester which is the component (B) constituting thecopolyester (B) comprehends a condensation product of a dicarboxylicacid and a diol through ester bonding, and a product of a hydroxy acidby self-condensation.

An example of the structure of the condensation product of dicarboxylicacid and diol by ester bonding among the components (B) is shown by theformula:

    H[O(CH.sub.2).sub.n OOC(CH.sub.2).sub.m COO].sub.p H

and preferably at least one terminal group has a hydroxyl group (OH).

In the above formula, n and m are usually 2 or more, preferably 2 to 12.

Also, p in the above formula is usually 10 or more, preferably 30 ormore, more preferably 50 to 100. If p is less than 10, the heatresistance at the time of polymerization and the copolymerizationproportions cannot be raised and the modification becomes insufficient.However, if p exceeds 200, it becomes difficult to conduct thepolymerization uniformly since the viscosity at the time of thepolymerization becomes high, and accordingly a variation in the physicalproperties of the obtained copolyester is easy to occur.

Examples of the acid component in the above formula are, for instance,organic dicarboxylic acids such as adipic acid, maleic acid and linoleicacid. Also, examples of the alcohol component are, for instance, organicdiols such as ethylene glycol, propylene glycol, butylene glycol, hexaneglycol, diethylene glycol and triethylene glycol. Further, as thealiphatic polyesters obtained from them, there are mentioned, forinstance, polyethylene adipate, polyhexylene adipate, polypropyleneadipate, polybutylene adipate, and the like.

In case of the aliphatic polyesters having hydroxyl groups at the bothends, the molar ratio of the hydroxyl group in the polymerization systemincreases in proportion to increase in the proportion of the aliphaticpolyester to be copolymerized, and the molar ratio of carboxylgroup/hydroxyl group deviates from 1. If so, the degree ofpolymerization in the polylactic acid unit does not sufficientlyincrease, resulting in production of only polymers having a smallmolecular weight and a weak strength.

Therefore, in case of using usual aliphatic polyesters having hydroxylgroups at the both ends as the component (B), it is preferable to addother dicarboxylic acids to the Polymerization system in order to bringthe hydroxyl group/carboxyl group molar ratio in the Polymerizationsystem near 1.

Also, as the alcohol component, there can be used an alcohol having ahigh molecular weight (number average molecular weight of not more than20,000, preferably 2,000 to 10,000) such as polyethylene glycol,polypropylene glycol, polybutylene glycol, polyethylene triol,polypropylene triol, or Polypropylene-polyethylene triol. Further, therecan be used a product prepared by addition of ethylene oxide to apolyhydric alcohol having a tri or more valency as used in thecopolyester (A).

The copolyesters with an aliphatic polyester having a branch tend tohave enhanced impact resistance and heat stability. Also, the presenceof the aliphatic polyester component different from the lactic acidcomponent in the molecular chain enables to control the crystallinityand biodegradability. In case of the aliphatic polyester containing alactic acid component, the efficiency of initiator is increased, thus itis possible to obtain a uniform lactic acid polymer having a highermolecular weight.

Also, in case that the other end group is carboxyl group, there is theadvantage that the carboxyl group/hydroxyl group ratio in thepolymerization system does no change even if lactic acid iscopolymerized with an optional amount of the aliphatic polyester, thusthe degree of polymerization is not lowered.

The aliphatic polyester having a hydroxyl group at one end and carboxylgroup at the other end can be prepared by self-condensation of a hydroxyacid or by condensation of the above-mentioned dicarboxylic acid anddiol.

The component (B) having carboxyl groups at the both ends can beobtained by raising the proportion of the dicarboxylic acid in theabove-mentioned condensation of dicarboxylic acid and diol.

The self-condensation products of hydroxy acids among the components (B)include products obtained by ring opening of a cyclic lactone onto analcohol. Thus, the aliphatic polyester comprehends those obtained byaddition of a cyclic lactone to a starting material for causing thering-opening of the cyclic lactone, e.g., water or ethylene glycol,bisphenol A, an alkylamine having a C₁ to C₂₀ alkyl group, or a tri- ormore valent compound such as glycerol, trimethylolpropane,pentaerythritol, sorbitol or castor oil. For instance, in case of thealiphatic polyester having a branch, the impact resistance and the heatresistance are improved.

Examples of the cyclic lactone are cyclic dimers of α-hydroxycarboxylicacids other than lactic acid, a cyclic dimer of glycolic acid(glycollide), caprolactones, glucono-1,5-lactone, and the like.

The molecular weight of the aliphatic polyester (B) is usually at least1,000, preferably at least 1,500, more preferably 1,500 to 20,000, interms of weight average molecular weight.

In case that the molecular weight of the component (B) is lower than1,000, it is necessary to increase the proportion of the aliphaticpolyester copolymerized upon modification. In this case, the lowering ofthe crystallinity of PLLA is marked, and lowering of the strength andheat resistance and increase of discoloration are easy to occur, thusfavorable.

On the other hand, if the molecular weight of the component (B) exceeds20,000, oxidation of the obtained copolyester (B) is easy to occur, andfiber strength and a color are easy to change with the lapse of time,thus unfavorable.

Explanation of the process for preparing the copolyester (B) is omitted,since the apparatus, procedure, optionally used antioxidant andcatalyst, and the like are the same as the case of copolyester (A)except that the component (A) used in the preparation of the copolyester(A) is substituted by the component (B).

Also, the molding process and uses of the copolyester (B) are the sameas the case of the copolyester (A) and, therefore, the explanationthereof is omitted.

Next, an explanation is given below with respect to the copolyesters ofthe lactic acid component and the component (C) (hereinafter alsoreferred to as "copolyester (C)").

With respect to the proportions of the lactic acid and the component (C)in the copolyester (C), the proportion of the component (C) in thecopolyester (C) is 0.5 to 20% by weight, preferably 1 to 20% by weight,more preferably 2 to 15% by weight, still more preferably 3 to 10% byweight. The higher the content of the component (C), the crystallinityis much lowered to decrease the fragility and to increase the impactresistance (first effect).

Further, an important change in physical properties by introduction ofthe component (C) is an increase in the rate of degradation (secondeffect). The degradation rate is also produced by the lowering of thecrystallinity resulting from copolymerization, but it is assumed thatfurther effect based on the hydrophilic property of the sulfo group isparticularly large. In both cases, the alkali metal salts (sodium salt,potassium salt, etc.) of sulfo group exhibit more marked effect thansulfo group itself.

The third effect of the introduction of the component (C) is animprovement in the dyeing property. The polylactic acid is dyeable witha disperse dye, but is poor in color fastness (migration phenomenon ofdye owing to wet friction and heating). Thus, the improvement has beendesired for use as clothes and non-cloth fibers. Vivid dyeing with basicdyes is enabled and color fastness is improved by the introduction ofsulfo group.

The molecular weight of the copolyester (C) is at least 50,000,preferably 60,000 to 300,000, more preferably 80,000 to 200,000, interms of average molecular weight. If the average molecular weight isless than 50,000, the fibers, films and molded articles lack instrength. Since the melt viscosity is increased by the introduction ofsulfo group, copolyesters having a relatively low molecular weight(50,000 to 80,000) can also be used.

The copolyester (C) contains the lactic acid as a main component, namely99.5 to 80%, preferably 80 to 99%, more preferably 85 to 98%, still morepreferably 90 to 97%, of the lactic acid component. The lactic acidcomponent comprehends those derived from L-lactic acid, D-lactic acid,and an L/D-lactic acid mixture. Since an L/D-copolymer generally lowerscrystallinity and heat resistance, a polymer of either one of opticallyactive monomers is preferable. In case of being mainly composed of theL-form, it is desirable that the content of the L-form is usually notless than 80% (not more than 20% of the D-form), preferably not lessthan 90%, more preferably not less than 95%. Similarly, in case of beingmainly composed of the D-form, it is desirable that the content of theD-form is usually not less than 80%, preferably not less than 90%, morepreferably not less than 95%.

Next, an explanation is given below with respect to the component (C).

The component (C) is a sulfo group-containing ester-forming compoundrepresented, for instance, by the formula (I): ##STR1## wherein X¹ andX² are an ester-forming group, A is a trivalent aromatic group, and M isa metal atom or a hydrogen atom; or by the formula (II): ##STR2##wherein X ¹ and X² are an ester-forming group, A is a trivalent aromaticgroup, P is a phosphorus atom, and R¹, R², R³ and R⁴ are an alkyl grouphaving 1 to 15 carbon atoms or an aryl group having 6 to 20 carbonatoms.

Examples of the compound (I) are, for instance, a metal-sulfonatedbenzene dicarboxylic acid or its alkyl ester (alkyl group having 1 to 15carbon atoms) such as sodium 5-sulfoisophthalate, dimethyl sodium5-sulfoisophthalate, potassium 5-sulfoisophthalate, dimethyl potassium5-sulfoisophthalate, diethyl potassium 5-sulfoisophthalate, lithium5-sulfoisophthalate, dimethyl lithium 5-sulfoisophthalate or sodium2-sulfoterephthalate; a metal-sulfonated naphthalene dicarboxylic acid,its alkyl ester (alkyl group having 1 to 15 carbon atoms) or its esterwith a lower diol having 2 to 8 carbon atoms, such as sodium4-sulfo-2,6-naphthalene dicarboxylic acid, dimethyl sodium4-sulfo-2,6-naphthalene dicarboxylic acid, sodium4-sulfo-1,4-naphthalene dicarboxylic acid or sodium5-sulfo-1,4-naphthalene dicarboxylic acid; and the like.

Examples of the compound (II) are, for instance, tetrabutylphosphonium3,5-dicarboxybenzenesulfonate, ethyltributylphosphonium3,5-dicarboxybenzenesulfonate, benzyltributylphosphonium3,5-dicarboxybenzenesulfonate, phenyltributylphosphonium3,5-dicarboxybenzenesulfonate, tetraphenylphosphonium3,5-dicarboxybenzenesulfonate, butyltriphenylphosphonium3,5-dicarboxybenzenesulfonate, benzyltriphenylphosphonium3,5-dicaboxybenzenesulfonate, tetrabutylphosphonium3,5-dicarbomethoxybenzenesulfonate, ethyltributylphosphonium3,5-dicarbomethoxybenzenesulfonate, tetraphenylphosphonium3-carboxybenzenesulfonate, their alkyl esters (alkyl group having 1 to15 carbon atoms), their esters with a lower diol having 2 to 8 carbonatoms, and the like.

One kind of, or two or more kinds of the sulfo group-containingester-forming compound represented by the formula (I) or (II) may beincluded in the copolyester (C). Preferable examples of the sulfogroup-containing ester-forming compound are 5-sulfoisophthalic acid,5-sulfoterephthalic acid, their salts with an alkali metal or the like(for example, potassium, sodium, lithium, ammonium, an alkylphosphonium,etc.), their esterification products wherein their carboxyl groups atthe both ends are esterified with a lower diol having 2 to 4 carbonatoms such as ethylene glycol or propylene glycol.

The copolyester (C) contains the lactic acid component as the maincomponent and the component (C) as the comonomer component, and it mayfurther contain known diols or dicarboxylic acids as the thirdcomponent.

Examples of the above-mentioned diols are, for instance, ethyleneglycol, propylene glycol, butanediol, hexanediol, octanediol,decanediol, cyclohexanediol, diethylene glycol, triethylene glycol, andthe like.

In particular, if the diols are linear diols having 6 or more carbonatoms, they may contain a branched chain, but preferably the size of thebranched chain is one having 3 or less carbon atoms and the number ofbranched chains is 2 or less since lowering in strength and heatresistance of the obtained fibers is brought about if the crystalstructure of the fibers is disturbed excessively.

Also, the strength and heat resistance of the obtained fibers are alsolowered if the number of carbon atoms of the linear diols is too largeand, therefore, the number of carbon atoms of the linear chain ispreferably at most 15, more preferably at most 12. Also, an unsaturatedbond may be included in the carbon chain.

Examples of the above-mentioned dicarboxylic acids are succinic acid,adipic acid, sebacic acid, decanedicarboxylic acid, terephthalic acid,isophthalic acid and other dicarboxylic acids.

In particular, difunctional carboxylic acids having 6 or more carbonatoms may contain a branched chain if the number of carbon atoms oflinear chain is 6 or more. However, if the crystal structure of fibersis disturbed excessively, it causes lowering in the strength and heatresistance of the fibers, and for this reason, the size of the branchedchain is preferably that the number of carbon atoms is 3 or less, andthe number of branched chains is preferably 2 or less.

Also, the strength and heat resistance of the obtained fibers are alsolowered if the number of carbon atoms of the linear chain is too large.Thus, the number of carbon atoms of the linear chain is preferably atmost 15, more preferably at most 12.

Examples of such a difunctional carboxylic acid are a saturatedaliphatic dicarboxylic acid such as adipic acid, azelaic acid or sebacicacid, and an unsaturated aliphatic dicarboxylic acid such as fumaricacid or citraconic acid.

A cyclic carboxylic acid such as caprolactone, pivarolactone oroctanolactone can also be used.

The process for preparing the copolyester (C) is explained below.

It is fairly difficult to copolymerize the lactic acid component withnot less than 0.5% of sulfoisophthalic acid based on the lactic acidcomponent, since sulfo group (particularly metal salt thereof) ishygroscopic and the water content is high and, therefore, contaminationof the polymerization system of lactic acid component with water causeshydrolysis of the polymer, so no high degree of polymerization isobtained.

However, if other aliphatic polyester-forming components having arelatively high stability and sulfoisophthalic acid are previouslyreacted in a sufficiently dehydrated state (vacuum) and the obtainedprepolymer (oligomer or polymer) containing sulfo group (less water) isreacted with the lactic acid component, the copolymerization can beachieved relatively easily.

In case of this method, it is preferable that the both end groups or oneend group of the sulfo group-containing prepolymer molecule is hydroxylgroup. For this purpose, it is desirable that, in the synthesis of thesulfo group-containing prepolymer by esterification, the molar ratio ofcarboxyl group and hydroxy group is equimolar ratio or the hydroxylgroup is excess by about 0.1 to about 30%.

The sulfo group-containing prepolymer and the lactic acid component canbe polymerized in a solvent, but the melt polymerization is the mostefficient. In case of the melt polymerization, the lactic acid componentis polymerized at a temperature of not more than about 220° C. (if thetemperature is too high, a decomposition reaction is accelerated).Therefore, it is preferable that the prepolymer has a melting point ofnot more than 220° C., especially not more than 200° C.

The sulfo group-containing prepolymer can be obtained by subjecting thesulfo group-containing ester-forming compound (I) or (II) toesterification with a lower diol having 2 to 4 carbon atoms such asethylene glycol, propylene glycol or diethylene glycol, and/or bysubjecting this esterification product to condensation. For example, theprepolymer having the lowest molecular weight is a reaction product ofone molecule of the sulfo group-containing compound with two moleculesof the diol, and examples thereof are, for instance, bishydroxyethylsulfoisophthalate, bishydroxybutyl sulfoisophthalate, bishydroxyhexylsulfoisophthalate, and the like. If dehydration is sufficientlyconducted, it is also possible to react lactic acid with a lactide.

The reaction product of two molecules of the sulfo group-containingester-forming compound with 3 molecules of the diol is an oligomer whichis an example of the above-mentioned prepolymers. The weight averagemolecular weight of the prepolymer is from 700 to 30,000, especially1,000 to 20,000, more especially 1,000 to 10,000. The weight proportionof the above-mentioned sulfo group-containing compound in the prepolymeris usually from 10 to 80%, preferably 30 to 60%.

For instance, in case that the hydroxyl groups at the both ends of aprepolymer having a weight average molecular weight of 10,000 andcontaining 40% of a sulfo group-containing ester-forming compound serveas a polymerization initiating sites and a lactide is polymerized,assuming that the molecular weight of each of the polylactide(polylactic acid) portions is 80,000, the molecular weight of the entireis 170,000 and the content of the sulfo group-containing compoundbecomes 2.4%. Similarly, if the molecular weight of the polylactideportion is 40,000, the molecular weight of the entire is 90,000 and thecontent of the sulfo group-containing compound becomes 4.4%.

The copolyester (C) Can be prepared by reacting the lactic acidcomponent with a compound containing the sulfo group-containingester-forming compound and having 2 ester-forming functional groups(hydroxyl group, carboxyl group or the like) per molecule. As mentionedabove, a prepolymer obtained by reacting sulfoisophthalic acid withother polyester-forming material is particularly preferred as thecompound containing the sulfo group-containing ester-forming compoundand having 2 ester-forming functional groups. In order to obtain thecopolyester having a higher molecular weight, to the raw materials forthe polymerization may be further added a slight amount (not more than1%) of a trifunctional component (a triol such as glycerol, hydroxyglutalic acid or benzene triol; a terminal-esterification product of atricarboxylic acid such as trimellitic acid with ethylene glycol, etc;and the like).

The polymerization may be carried out by a melt polymerization method ora solvent method using a solvent, but there are many cases where themelt polymerization method is better from the viewpoints of safety andefficiency.

Batchwise type and continuous type reactors capable of conductingheating, agitation, pressure reduction or the like can be used as apolymerization vessel used in the preparation of the copolyester (C). Incase of carrying out the polymerization of the lactic acid component bya thermal polymerization of lactide, a twin-screw heading extruderequipped with a vent, which effectively achieves heating, agitation andsending of reaction products and also can achieve pressure reduction, isadvantageous, and a plurality thereof may be connected in series asoccasion demands.

Upon the preparation of the copolyester (C), there may be incorporatedand mixed, as occasion demands, above-mentioned or the like catalyst,antioxidant, ultraviolet absorber, lubricant, pigment, colorant,inorganic particles, antistatic agent, releasing agent, and well-knownother organic and inorganic additives and fillers.

The preparation of the copolyester (C) using the twin-screw kneadingextruder equipped with a vent or the like apparatus can be made in thesame manner as the case of the copolyester (A) by using the component(C) instead of the component (A) used in the preparation of thecopolyester (A), preferably by using a prepolymer containing thecomponent (C).

Also, since the molding process and uses of the prepared copolyester (C)are the same as the case of the copolyester (A), the explanation thereofis omitted.

The molded articles of the present invention will be explained below.

The molded articles of the present invention are those prepared bymelt-molding the biodegradable copolyesters of the present invention asmentioned above.

Examples of the above-mentioned molded articles are, for instance, aconjugate fiber composed of (a) a biodegradable (co)polyester having amelting point Ta used gin melt-adhesive polylactic acid fibers or thelike [hereinafter also referred to as "(co)polyester (a)"; the term"(co)polyester" meaning both a polyester and a copolyester], and (b) abiodegradable (co)polyester [hereinafter also referred to as"(co)polyester (b)"] which has a melting point lower than Ta by at least10° C. or which is amorphous and has no melting point [hereinafter alsoreferred to as "molded article (I)"]; a molded article comprising asheath and a core, wherein the sheath is made of a less degradablecopolyester that the rate of degradation by biodegradation or byhydrolysis in neutral water or aqueous solution is low, and a core ismade of a biodegradable copolyester having a rate of degradation of atleast 2 times the rate of degradation of the above-mentioned sheath, andboth the core component and the sheath component aremolecular-orientated [hereinafter also referred to as "molded article(II)"]; a conjugate fiber composed of the above-mentioned biodegradablecopolyester and a fiber-forming copolyester containing at least 40% of acomponent derived from an aromatic compound, wherein the fiber-formingcopolyester is separated by the biodegradable copolyester into aplurality of segments in the transverse section of the monofilament, atleast a part of the fiber surface is occupied by the biodegradablecopolyester, and the conjugate fiber is dividable [hereinafter alsoreferred to as "molded article (III)"]; and the like.

As the (co)polyester (a) in the molded article (I), there is preferred apolylactic acid polymer containing at least 80% of L-lactic acid unitsor D-lactic acid units (including the biodegradable copolyester of thepresent invention).

It is known that optical isomers, D-form and L-form are present inlactic acid. If the both are copolymerized, the melting point islowered, and if the optical purity is not so high, the product becomesan amorphous polylactic acid which no longer show a melting point. Theoptical purity (proportion of the D-form or L-form) of the lactic acidunits in the (co)polyester (a) is preferably at least 80% by mole, morepreferably at least 95% by mole, still more preferably at least 98% bymole.

In contrast, as the (co)polyester (b) (which can be the biodegradablecopolyester of the present invention) used in the molded article (I),crystalline one having a melting point Tb is preferred in that the heatresistance is superior, but amorphous one having no melting point may beused. In case that the (co)polyester (b) has a melting point Tb, themelting point Tb is a temperature lower than the above-mentioned meltingpoint Ta by at least 10° C., and the difference in melting point betweenthem is preferably from 10° to 80° C., more preferably 30° to 60° C.

The copolyester (b) which has a low melting point or is amorphous, isobtained by a method wherein the optical purity of the lactic acid unitsin the copolyester (b) is controlled. That is to say, if the opticalpurity is lowered, copolyesters having a low melting point are obtained,and amorphous ones can be obtained by further lowering the opticalpurity.

In general, L-form is produced when lactic acid is manufactured by afermentation method, and for industrial purposes L-lactic acid is easyto obtain inexpensively in a large quantity rather than D-lactic acid.Accordingly, the polylactic acid-based (co)polyesters of the presentinvention are usually those mainly made of L-lactic acid. However, withrespect to polymers mainly made of D-lactic acid too, those havingsimilar physical properties to the case of L-lactic acid can beobtained.

As the (co)polyester (a) and/or the (co)polyester (b) used in the moldedarticles (I), there can also be used polylactic acid-based copolymersproduced by copolymerization of lactic acid and polyethylene glycol(PEG) having a number average molecular weight of at least 300. In thiscase, the content of polyethylene glycol in the copolymers is preferablyfrom about 0.1 to about 15%.

Also, the (co)polyester (a) and/or the (co)polyester (b) may becopolymerization products containing preferably 0.1 to 15%, morepreferably 0.1 to 10%, still more preferably 0.5 to 7%, of a compoundhaving a plurality of functional groups, e.g., a polyhydric aliphaticalcohol (such as ethylene glycol, propylene glycol, butanediol,hexamethylenediol, glycerol, trimethylolpropane, penthaerythritol,sorbitol or castor oil), a polyhydric alicyclic alcohol (such ascyclohexanediol, cyclohexanedimethanol, cycloheptanediol orcycloheptanedimethanol), an aliphatic polycarboxylic acid (such asadipic acid, sebacic acid, decanedicarboxylic acid, citric acid,glutamic acid or aspartic acid), an alicyclic polycarboxylic acid (suchas cyclohexanedicarboxylic acid, cycloheptanedicarboxylic acid,cyclooctanedicarboxylic acid or cyclododecanedicarboxylic acid), analiphatic hydroxycarboxylic acid (such as L-lactic acid, D-lactic acid,glycolic acid, ε-hydroxycaproic acid, 3-hydroxybutyric acid,4-hydroxybutyric acid, hydroxystearic acid, recinoleic acid, malic acidor serine), an alicyclic hydroxycarboxylic acid, or an aromatichydroxycarboxylic acid (such as hydroxybenzoic acid); a lactone (such aslactide, glycollide, caprolactone or gluconic lactone); a cycliccompound such as a cyclic ether; and the like. By introducing thesepolyfunctional compounds or cyclic compounds, the fluidity ofcopolyesters in melt spinning is improved, so it is possible tocontemplate an improvement in spinning property, spinning workabilityand quality.

In the present invention, in order to obtain good-quality fibers havinga uniformity and a high strength, the molecular weight of the(co)polyester (a) is preferably not less than 50,000, more preferablynot less than 100,000, further more preferably not less than 150,000.Further, in order to form into uniform fibers and uniform fiberarticles, the difference in the molecular weight between the(co)polyester (a) and the (co)polyester (b) is preferably not more than50,000, more preferably not more than 30,000. If the difference in themolecular weight between the (co)polyester (a) and the (co)polyester (b)exceeds 50,000, there is a tendency of lacking in molding stability suchas spinning stability, so the quality of the obtained shaped articlessuch as fibers becomes easy to fluctuate, thus the variation becomeslarge to produce a possibility of impairing the commercial value.

In case that the molded article (I) is a conjugate fiber having amulti-layer structure of the (co)polyester (a) and the (co)polyester(b), examples of its structure in the transverse section are,core-sheath type, parallel type (side-by-side type), multi-core type,multi-parallel type (stripe type), concentric circle type, eccentriccircle type, and radial type structures. In any of the transversesectional structures, the conjugate fiber has a structure such that the(co)polyester (b) comes out to the fiber surface at least a part of thefiber surface. If the (co)polyester (b) does not appear at the fibersurface, the heat welding property is not exhibited, so the objects ofthe present invention cannot be achieved. Therefore, in case of theconjugate fiber of core-sheath structure in transverse section, the coreportion is made of the (co)polyester (a) and the sheath portion is madeof the (co)polyester (b).

The proportion of the portion made of the (co)polyester (a) in theabove-mentioned conjugate fiber is preferably not less than 50%, morepreferably not less than 60%, still more preferably not less than 70%,and it is desirable that the proportion is not more than 95%. Theconjugate fibers as mentioned above are prepared usually by conducting amelt spinning through special spinning nozzles designed to giverespective transverse section structure.

A non-woven fabric can be obtained by subjecting the molded article (I)(a heat weldable polylactic acid fiber) to entwinement into a non-wovenfabric form, and heating it by an embossing machine under pressure at atemperature which is higher than the melting point of the (co)polyester(b) if the (co)polyester (b) has a melting point, and is lower than themelting point of the (co)polyester (a), whereby the (co)polyester (b) isfused while the (co)polyester (a) keeps its original shape, and is fusedtogether with the (co)polyester (b) of adjacent other fibers.

Now referring to the molded article (II), the conjugate fibers in themolded article (II) are those prepared by a method wherein a pluralityof components are spun out with being joined together at the time ofspinning to form a single filament. The core-sheath conjugate fiber hasa composite structure such that a core component (polymer) is completelycovered with a sheath component (polymer).

FIGS. 5 to 11 are illustrative transverse sectional views of singlefibers showing various instances of a core-sheath conjugate fiber whichis one of the molded articles (II).

In FIGS. 5 to 11, numeral 26 is a sheath made of a slightly degradable(co)polyester, and numerals 27, 27A and 27B are a core made of an easilydegradable (co)polyester (which may be the biodegradable copolyester ofthe present invention). Numeral 28 is a hollow portion.

The less degradable (co)polyester used in the sheath portion of themolded article (II) can be selected in general from polyesters havingthe features such that (1) the purity is high, (2) the regularity andcrystallinity of structure are high, and (3) the content of an aromaticcomponent is higher. Its half-life (period until the tensile strength ofa fiber becomes 1/2) is usually within the range of about 1 month toabout 10 years, and the most commonly used half-life is from 1 to 5years.

As the less degradable (co)polyester for use as the sheath component,useful is a homopolymer containing no impurity (comonomer and mixture)such as poly(L-lactic acid), poly(D-lactic acid),poly(L-hydroxybutyrate), poly(D-hydroxybutyrate) or the like, or amodified product of which impurity content is small (less than 3%).Similarly, there is also useful a copolymerization product of a smallamount, e.g. 3 to 30%, of an aliphatic polyester component as adegradable component with a copolyester wherein a third component suchas isophthalic acid is introduced into an aromatic polyester such aspolyethylene terephthalate (hereinafter referred to as "PET"),polybutylene terephthalate (hereinafter referred to as "PBT") orpolyhexaneterephthalate (hereinafter referred to as "PHT").

Examples of the aliphatic polyester component used in theabove-mentioned less degradable (co)polyester are (1) a combination ofan aliphatic glycol (e.g. ethylene glycol, propylene glycol, butyleneglycol, hexanediol, octanediol or decanediol) and an oligomer ofethylene glycol (e.g. diethylene glycol or triethylene glycol) with analiphatic dicarboxylic acid (e.g. succinic acid, adipic acid,hexanedicarboxylic acid or decanedicarboxylic acid), (2) a lactone (e.g.caprolactone or pivalolactone) and (3) a hydroxycarboxylic acid (e.g.lactic acid, butyric acid or valerianic acid), and also, for instance,polylactic acid, polyhydroxybutyrate, polyethylene adipate, polybutyleneadipate, polyhexane adipate, polycaprolactone and copolymers containingthem.

Another example of the slightly degradable (co)polyester for theabove-mentioned sheath component is a material wherein the degradabilityis decreased by incorporating a water repellent component.

Examples of the water repellent component are a paraffin (liquidparaffin, natural paraffin, etc.), a wax (microcrystalline wax, etc.), ahigher fatty acid ester (butyl stearate, castor oil, ethylene glycolmonostearate (fatty acid glycol ester), etc.), an amide wax (stearicacid amide, palmitic acid amide, methylenebisstearoamide,ethylenebisstearoamide, oleic acid amide, etc.), a higher fatty acidmetal salt (stearic acid salt, lauric acid salt, etc., particularlycalcium salt, magnesium salt, zinc salt, etc.), polyethylene (weightaverage molecular weight not more than 20,000, especially not more than10,000 and not less than 2,000), polyethylene wax (molecular weight of1,500 to 2,000), etc.), silicone oil, silicone wax, and the like.

The mixing rate of the water repellent component is from about 0.1 toabout 5%, and in particular there are many cases where a range of 0.2 to3% is preferable.

The slightly degradable (co)polyesters for sheath use are advantageousto be subjected to a melt composite spinning with the core componentfrom the viewpoints of quality, properties and cost. Therefore, thosehaving a melting point (and melt viscosity) close to the melting point(and melt viscosity) of the easily degradable (co)polyester for core useare desirable. That is to say, it is desirable that the melting point ofthe sheath component is from 100° to 220° C., especially 120° to 200° C.

In case of using an aliphatic polyester such as polylactic acid orpolyhydroxybutyrate as the slightly degradable (co)polyester for sheathuse, the higher the molecular weight and regularity in molecularstructure of the aliphatic polyester which is unmodified (homopolymer),the higher the crystallinity and the lower the rate of degradation.Similarly, the rate of degradation can be decreased by drawing at a highdraw ratio to raise the degree of orientation and the degree ofcrystallization, or by subjecting to a heat treatment to raise thedegree of crystallization. Conversely, if the regularity in molecularstructure is decreased to lower the crystallinity by copolymerizing ormixing with second and third components, the rate of degradation isincreased.

As stated above, it is possible to control the rate of deterioration ofthe sheath component within a wide range by changing (1) the compositionof the polymer, particularly the ratio of the aliphatic component andthe aromatic component, (2) adding the water repellent component, or (3)factors such as crystallinity. For example, by changing the half-life ofthe sheath component embedded in the soil such as 2 weeks, one month, 3months, 6 months, 1 year, 2 years, 5 years or 10 years, the life(application limit period) of the conjugate fibers can be adjusted in awide range and it is possible to apply them to various uses.

On the other hand, with respect to the easily degradable (co)polyestersfor use in the core component of the molded articles (II), those havinga rate of degradation faster than that of the sheath component (rate ofdegradation of at least 2 times) are selected generally from (1) anon-modified aliphatic polyester, (2) a copolyester or mixturecontaining an aliphatic polyester as the main component and (3) anaromatic polyester copolymerized or mixed with an aliphatic polyester soas to impart a degradability thereto.

For core use, it is easy to lower the regularity in molecular structureof the polymer by copolymerization or mixing with the second and thirdcomponents or in a like manner in order to raise the rate ofdegradation. For example, it is possible to remarkably lower thecrystallinity of an aliphatic polyester such as poly-L-lactic acid orpoly-L-hydroxybutyrate or to make it amorphous by copolymerization with1 to 50%, especially 3 to 20%, of an optically active isomeric monomer(D-form). Similarly, the crystallinity can also be remarkably reduced byintroducing a different kind of an aliphatic component or an aromaticcomponent by means of copolymerization. Similarly, the crystallinity canalso be easily reduced by mixing with 1 to 50%, especially 3 to 20%, ofan oligomer of the same or different kind of monomer, or a differentkind of polymer.

In general, the degradability of a polymer tends to be increased if thepolymer is made hydrophilic, and tends to be decreased if the polymer ismade hydrophobic. The process for reducing the degradability by mixing awater repellent component has been explained in the above-mentioned itemconcerning a means for reducing the rate of degradation of the sheathcomponent. Conversely, the rate of degradation of polymers can beincreased by introducing a hydrophilic component. For example, the rateof degradation of polymers can be increased by copolymerization ormixing with a compound having amino group, imino group, amido bond,hydroxyl group, sulfo group, phosphoric acid group or ether bond. Forexample, it is possible to raise the rate of degradation bycopolymerization with about 0.5 to about 30% of sulfoisophthalic acid ora polyether, especially polyethylene glycol. Similarly, it is possibleto raise the rate of degradation by mixing with about 0.5 to about 30%of a polysuccharide or a polyamino acid.

Similarly, the rate of degradation of polyesters can be raised bycopolymerization or mixing with about 0.5 to about 30% of a componenthaving a low glass transition temperature (Tg), e.g., a component havinga Tg of not more than 20° C., especially not more than 0° C., (forexample, polycaprolactone, polyhexane adipate, polyalkylene ether, orthe like).

As stated above, it is possible to control the rate of degradation ofthe core component within a wide range by changing (1) the compositionof the polymer, particularly the ratio of the aliphatic component andthe aromatic component, or (2) factors such as crystallinity, or byintroducing (3) a hydrophilic component or (4) a component having a lowTg. For example, by changing the half-life of the sheath componentembedded in the soil such as one week, 2 weeks, one month, 2 months, 6months, 1 year or 2 years, the deterioration performances afterexceeding the term of validity can be adjusted in accordance with thepurpose of application. The half-life of the core component variesdepending on the purposes, but there are many cases that a half-life ofnot more than 6 months, especially not more than 3 months, moreespecially 1 to 3 months, is preferable. However, if the core componentis easy to be degraded too much, a care should be taken since the coremay be degraded prior to breakdown of the sheath by water or the likepenetrating through the sheath.

The (co)polyesters used in the sheath and the core of conjugate fiberswhich are the molded article (II) may contain, as occasion demands,antioxidant, ultraviolet absorber, lubricant, pigment, colorant,antistatic agent, releasing agent, and other well-known additives andfillers.

FIGS. 5 to 11 are views for illustrating concrete examples of thetransverse section of conjugate fibers, any of which are the moldedarticle (II). FIG. 5 shows an example of a concentric circle type, FIG.6 shows an example of an eccentric type, FIG. 7 shows an example of adouble core type, FIG. 8 shows an example of a non-circular type, FIG. 9shows an example of a multi-core deformed shape type, FIG. 10 shows anexample wherein two kinds of easily degradable (co)polyesters (2A) and(2B) integrally form a core, and FIG. 11 shows an example of a hollowtype. That is to say, the conjugate fibers in the molded articles (II)may have any of structures such as concentric structure, eccentricstructure, single core structure and multi-core structure. The shape ofthe section can also be suitably selected, such as circle, non-circle(ellipse, polygon, multi-blade shape, star shape, C-shape, I-shape,H-shape, L-shape, W-shape, cocoon shape, and similar shapes thereto) andhollow shape.

The sheath/core ratio (sectional area ratio or volume ratio) of theconjugate fiber in the molded article (II) is selected in accordancewith the purposes and uses. Preferably, the ratio is from 2/1 to 1/20,especially from 1/1 to 1/10, more especially from 1/1 to 1/4. The lifeof the conjugate fiber is determined mainly by the rate of deteriorationof the sheath component and the thickness of the sheath. In case ofaltering the life according to the purposes and uses, it is much easierand advantageous to change the ratio so as to change the thickness ofthe sheath rather than preparing many sheath components having adifferent deterioration rate. In order to exhibit the features of themolded article (II), namely the characteristics that the deteriorationis a little during the use (before the life duration) and rapidlyproceeds after reaching the life, it is preferable that the rate ofcontribution of the core component to the strength of the conjugatefiber is not less than 30%, especially not less than 40%, moreespecially not less than 50%. The thickness of the sheath (in thethinnest portion) which is the most widely used is usually not less thanabout 0.5 μm and not more than about 100 μm, preferably 1 to 10 μm.

It is effective in sufficiently exhibit the features of the conjugatefiber which is the molded article (II) to make the ratio of thedeterioration rates of the core and sheath components large. This ratioof the deterioration rates is required to be at least 2, and ispreferably at least 5, more preferably at least 10, and the range ofabout 5 to about 200 is the most frequently utilized. The time until thevalue of tensile strength of a fiber is reduced to 1/2 of the initialvalue of the fiber (non-deteriorated) when the fiber is degraded ordeteriorated in the soil or water, namely the half-life of the strength(hereinafter referred to as "half-life"), is used as the index for therate of deterioration. Since in many cases the strength decreases almostlinearly with the lapse of time (up to the vicinity of the half-life),the half-life can be regarded as being inversely proportional to therate of deterioration. The deterioration rate ratio is represented bythe reciprocal of the ratio of the half-life values of the core andsheath components, wherein the half-life is obtained by a deteriorationtest of a single-component fiber prepared using each of the core andsheath components under substantially the same preparation conditions asthose of a conjugate fiber. For example, the half-life ratio (c/d ratio)for a component (c) having a half-life of 3 months and a component (d)having a half-life of 2 years is 1/8, and the deterioration rate ratiois 8.

Of course, the deterioration rate is a relative one differing dependingon the deterioration conditions. Even if using the same polymer, itbecomes "less degradable" or "easily degradable" if the testingconditions or the comparison object are altered. Therefore, the ratio ofdeterioration rates is determined by deteriorating the both componentsunder the same conditions. A suitable deterioration rate ratio can beselected according to the application purpose from a case of having beenembedded in the soil, a case of having been fermented in a compost, acase of having been immersed in a waste water treating vessel containingan active sludge, a case of having been immersed in sea water, a case ofhaving been immersed in an aqueous buffer solution (commercial product.)of pH 7.2 at 37° C. (known to be similar to embedding in the humanbody), and a case of having changed the temperature in theseenvironments (acceleration test).

An instance of a method of embedding in the soil (upland field soil) atordinary temperature (15° to 25° C.) is shown in Examples describedafter.

As the sheath and core components there are used those having an enoughor large difference in relative rate of degradation between the both.The difference in degradation rate is obtained by changing variousfactors as mentioned before, but the factors such as purity, degree ofmodification, crystallinity, etc. among them are basic factors. Fromsuch points of view, there are many cases that it is desirable that thecrystallinity of the sheath component is higher than that of the corecomponent by at least 5%, especially at least 10%.

Similarly, there are many cases that it is desirable that the meltingpoint of the sheath component (in case of an amorphous one, thesoftening point) is higher than that of the core component by at least5° C., especially at least 10° C.

It is desirable that the core component and the sheath componentstrongly adhere to each other. (Of course, even if they are poor inadhesion property, the conjugate fiber in the molded article (II) has amuch higher resistance to external force such as friction in comparisonwith a coating method, since the sheath component is also sufficientlydrawn and oriented.) A good adhesion is relatively easily obtained byusing akin (co)polyesters as the core and sheath components. Inparticular, a combination of (co)polyesters having the same maincomponent (component included in an amount of not less than 50%) andmodified by changing the amount of the secondary component gives a goodadhesion property. For example, there are many combinations showing anexcellent adhesion property in combinations of a homopolymer(modification rate 0%) and a copolymer containing it as a main component(modification rate 2 to 50%). Similarly, a combination of copolyestershaving modification rates of, for example, 3% and 10% is also aninstance of the combination showing a good adhesion property. A polymercontaining L-lactic acid as the main component and a polymer containingL-hydroxybutyrate as the main component have a similar molecularstructure to each other and they show a good adhesion property.

FIG. 12 is a view illustrating the deterioration characteristics of aconjugate fiber in the molded article (II). Curve 29 is a deteriorationcurve of a (co)polyester (e) having a high deterioration rate (half-lifeof 1 month), curve 30 is a deterioration curve of a (co)polyester (f)having a low deterioration rate (half-life of 2.5 years), and curves 31and 32 are deterioration curves of conjugate fibers comprising a core ofthe (co)polyester (e) and a sheath of the (co)polyester (f).

The curve 31 shows an instance wherein the sheath is thin, so the sheathis substantially destroyed after about 3 months and the deterioration ofthe core then rapidly proceeds, thus showing a half-life of about 4months. The curve 32 shows an instance wherein the thickness of thesheath is larger than that of the conjugate fiber in curve 31, so thesheath is substantially destroyed after about 5.5 months and thedeterioration of the core then rapidly proceeds to show a half-life of6.3 months. In curve 31 the life (period of use) is about 3 months, andin curve 32 the life is about 5.5 months. As understood from the figure,the conjugate fibers of the molded article (II) can possess veryfavorable deterioration characteristics such that they are not sodeteriorated during the use, and after exceeding the life they arerapidly deteriorated. On the other hand, conventional single-componentfibers have the disadvantage that the deterioration proceeds simply asshown by curves 29 and 30, so the strength remarkably decreases duringthe use or does not easily decrease even after the use. Also, in case ofa coating method, the coating film is easy to be damaged by friction orthe like, so it is very difficult to obtain, in a practical use, thecharacteristics as represented by curves 31 and 32 in FIG. 12.

The polymers used in the sheath and the core of the conjugate fibers ofthe molded article (II) are required to have a sufficient molecularweight in order to impart a sufficient strength to the fibers. Ingeneral, in many cases, it is preferable that the (co)polyesterscontaining an aliphatic component as a main component (not less than50%) have a molecular weight (average molecular weight in case of thebiodegradable copolyester of the present invention; weight averagemolecular weight in case of other (co)polyesters) of not less than30,000, preferably not less than 40,000, more preferably 60,000 to300,000. On the other hand, in case of the (co)polyesters containing anaromatic component as a main component (not less than 50%), there aremany cases that the weight average molecular weight is preferably notless than 15,000, more preferably not less than 20,000, still morepreferably 30,000 to 150,000.

The conjugate fibers sufficiently drawn of the molded article (II) areable to have usually a strength of not less than 2 g/d, and in manycases, to have a strength of not less than 3 g/d, more preferably notless than 4 g/d. Products having a high strength of not less than 6 g/dcan also be relatively easily obtained.

The melting point or softening point of the polymers used in the sheathand the core of the conjugate fibers of the molded article (II) ispreferably at least 100° C., more preferably at least 120° C., stillmore preferably at least 150° C., in order to impart a sufficient heatresistance to the fibers. However, in case of uses at low temperaturesother than normal uses or in case of purposes to impart a heatingweldability, polymers having a melting or softening point of not morethan 100° C. can be utilized.

The conjugate fibers of the molded article (II) can be prepared bywell-known multi-component fiber spinning methods such as melt spinning,dry spinning, wet spinning, and dry-wet spinning. Drawing, heattreatment, crimping and the like can also be conducted if needed. Inparticular, the melt spinning is preferable since it can be conducted ata high velocity and in a high efficiency. In particular, partiallyorientated yarns (POY) can be obtained by spinning at a spinningvelocity of at least 3,000 m/min., and highly orientated yarns (HOY) canbe formed by spinning at a spinning velocity of at least 5,000 m/min.Further, it is possible to continuously conduct polymerization-spinningby connecting with a polymerization step, and it is also possible tosimultaneously conduct the spinning and the drawing by a spin-drawmethod, thus they are very efficient.

The conjugate fibers of the molded article (II) as mentioned above haveexcellent features that (1) sufficient orientation and crystallizationof both the core portion and the sheath portion can be achieved bydrawing or ultra-high velocity spinning, etc., whereby an excellentstrength can be obtained, (2) control of the degradation rate can beconducted within a wide range, thus fibers having a low degradation rate(a long life) can also be easily obtained, (3) fibers being uniform inthe composite structure and the thickness of sheath and having no defectcan be easily obtained, thus the reliability of performances and qualityis high, (4) the life of the sheath can be easily and freely changed bychanging the thickness thereof, thus being applicable to wide ranges ofpurposes and uses, (5) the sheath and the core are prevented frompeeling off owing to friction or the like by combining components (e.g.akin polymers) having a good adhesion property between the sheath andthe core, and (6) the fibers can be prepared at a high velocity in ahigh efficiency, thus excellent in practicality and economicalefficiency.

Not only the biodegradable copolyesters of the present invention butalso any polyesters containing the lactic acid component as a maincomponent can be used in the conjugate fibers of the molded article(III).

The polyesters containing the lactic acid component as a main componentare polymers containing at least 50% of the lactic acid component suchas L-lactic acid and/or D-lactic acid, and comprehend poly-L-lactic acidhomopolymer, poly-D-lactic acid homopolymer, L-lactic acid/D-lactic acidcopolymer, and these polymers into which not more than 50% of a secondor third component is included by copolymerization or mixing. They areeasily degradable (co)polyesters.

The polyesters containing the lactic acid component as a main componentcan be obtained by adding not more than 50% of the second or thirdcomponent at the time of a melt polymerization, solvent polymerizationand ring-opening polymerization of the lactic acid component, andreacting them.

The polylactic acid that the lactic acid component is polymerized is ingeneral fairly stable in a dry state, but is easily hydrolyzed inneutral water or an aqueous solution (salts, etc.), or by action oforganisms or by a weak alkali (for example, at most 0.1% aqueoussolution of sodium hydroxide of pH at most 10), and the resulting lacticacid is further degraded with ease by organisms to convert finally intocarbon dioxide gas and water. Therefore, the conjugate fibers of themolded article (III) can be divided safely and easily by the action of aneutral or weakly alkaline solution or organisms without wastingresources and without causing environmental pollution.

Lactic acid used as the main component of the easily degradable(co)polyesters [(co)polyesters including the biodegradable copolyestersof the present invention] in the conjugate fiber of the molded article(III) is L-lactic acid, D-lactic acid or a mixture of L- and D-lacticacid, but L-lactic acid prepared by a fermentation method is inexpensiveand advantageous. Poly-L-lactic acid homopolymer and poly-D-lactic acidhomopolymer have a high crystallinity, and there are many cases thattheir rate of degradation in a neutral environment or by a biologicalaction is low. Consequently, in order to raise the rate of degradation,it is effective to introduce into poly-L-lactic acid, for example, 1 to50%, preferably 3 to 30%, more preferably 5 to 20%, of D-lactic acid bymeans of copolymerization. Similarly, it is also effective to introduceL-lactic acid into poly-D-lactic acid within the above range by means ofcopolymerization.

Similarly, it is possible to enhance the degradability by copolymerizingpoly-L-lactic acid or poly-D-lactic acid with 1 to 50% preferably 3 to30%, of a second component capable of forming ester bond, for example,lactones (such as pivalolactone, caprolactone, etc.), hydroxycarboxylicacids (such as lactic acid, glycolic acid, etc.), combinations ofglycols (for example, ethylene glycol, butanediol, hexanediol,octanediol, decanediol, and the like) and dicarboxylic acids (forexample, succinic acid, adipic acid, sebacic acid, and the like).

As the above-mentioned comonomer component, there are preferredaliphatic compounds which are easy to be biologically degraded, e.g. adiol such as ethylene glycol, butanediol, hexanediol, octanediol ordecanediol, a dicarboxylic acid such as succinic acid, adipic acid orsebacic acid, a hydroxycarboxylic acid, an aliphatic lactone, such aspivalolactone or caprolactone. Polyethylene glycol is also preferredbecause of having a biodegradability. Also, there can be utilizedpolymers having an adequate amount of branches or weak crosslinkagestherein, produced by reacting a slight amount (for example, than notmore 5% preferably not more than 2%) of a polyfunctional compound suchas glycerol, pentaerythritol, trimellitic acid or pyromellitic acid atthe time of polymerization for producing polymers containing the lacticacid component as a main component.

The easily degradable (co)polyesters in the conjugate fibers of themolded article (III) may contain materials other than polylactic acidand its copolymers as additives, for example, releasing agent, fluidityimprover, water repellent, agent for imparting hydrophilic property,stabilizer, antioxidant, pigment, colorant, various inorganic particlesand other improvers.

In general, polylactic acid is susceptible to hydrolysis, and when,after the melt polymerization thereof, it is cooled, solidified, formedinto chips, dried, molten again and spun, it frequently decreases themolecular weight by degradation. Of course, in case of the conjugatefiber, since the easily degradable (co)polyester containing the lacticacid component as a main component is removed by degradation in thepost-processing stage, the degree of polymerization on such a level ascapable of conducting a multi-component fiber spinning is sufficient forthe easily degradable (co)polyester. However, from the viewpoints ofspinnability and strength of the obtained conjugate fiber, it isdesirable that the easily degradable (co)polyester has a certain levelof high molecular weight (for example, a weight average molecular weightof at least 40,000, preferably not less than 60,000 and not more than300,000). It is also desirable to subject the produced polymer directlyto multi-component fiber spinning without cooling to solidify it afterthe melt polymerization.

The fiber-forming aromatic copolyesters which are the other constituentcomponent in the conjugate fiber of the molded article (III) are thosecontaining at least 40%, preferably at least 50%, more preferably atleast 60%, of the component derived from an aromatic compound. If thecontent is less than 40%, it is difficult to impart a heat resistance, astrength and a spinning property which are sufficient for forming thefiber.

As a polyester-forming aromatic compound, there are well known anaromatic dicarboxylic acid such as terephthalic acid, isophthalic acid,sulfoisophthalic acid or naphthalenedicarboxylic acid, an aromatichydroxydicarboxylic acid such as hydroxybenzoic acid, and an aromaticdiol such as bis-hydroxyethoxyphenyl methane. The fiber-forming polymerscontaining at least 40% of the aromatic compound component can beobtained by using these aromatic compounds in combination with analiphatic diol such as ethylene glycol, propanediol, butanediol,hexanediol or decanediol, an aliphatic dicaroboxylic acid such as adipicacid or sebacic acid, or an aliphatic lactone such as caprolactone. Forexample, copolymers containing polybutylene terephthalate (PBT) orpolyethylene terephthalate (PET) as a main component (at least 50%)copolymerized with other ester bond-forming components are useful as thearomatic polyester component for the conjugate fibers of the moldedarticle (III) in points of fiber-forming property, crystallinity andmelting point. By the way, PET is composed of 77% of an aromaticcomponent, PBT is composed of 67% of an aromatic component, and aPET/polyethylene adipate copolymer in a ratio of 60/40 is composed of46% of an aromatic component.

The above-mentioned aromatic copolyester containing at least 40% of thearomatic component is capable of forming fibers, and the fibers after adivision treatment and the fiber structures are desired to have astrength meeting the purposes. From this point of view and from thepoints of spinnability and drawing property, the aromatic copolyesterhaving a weight average molecular weight of at least 15,000, especiallyat least 20,000, is preferred. Of course, the aromatic copolyester musthave a sufficient strength even after the division of the conjugatefiber without being degraded in a neutral or weak alkaline environmentin which the easily degradable (co)polyester containing the lactic acidcomponent as a main component is degraded, or by an action of organisms.For example, it is preferable that the rate of degradation (weightreduction) of the aromatic copolyester when treated with an aqueousweakly alkaline solution (0.1% aqueous solution of sodium hydroxide, at25° C.) is not more than 1/10, especially not more than 1/50, of that ofthe easily degradable (co)polyester.

The composite structure in transverse cross section of the conjugatefiber of the molded article (III) is such that the aromatic copolyesteris divided into a plurality of segments by the easily degradable(co)polyester and at least a part of the fiber surface is occupied bythe easily degradable (co)polyester. As a result of having thisstructure, the conjugate fiber of the molded article (III) is dividedinto at least two filaments, preferably at least 3 filaments, morepreferably at least 4 filaments, by decomposing the easily degradable(co)polyester to remove it, whereby the fineness of the fiber is greatlydecreased and the softness and water absorbing property are increased.

The objects of dividing the conjugate fiber of the molded article (III)are (1) to form fine fibers, (2) to form ultra-fine fibers, (3) to formmodified cross-sections, (4) to form special cross-sections, (5) toimpart special functions, and the like. In case of the object of formingfine fibers, the number of segments of the aromatic copolyester in thesingle fiber section is from about 2 to about 8. In case of the objectof forming ultra-fine fibers, the number of segments is at least 8, forexample, from about 10 to about 100. In case of forming a modifiedcross-section, the transverse cross section of each of the segments canbe formed into polygon shape, star shape, multi-blade shape, flat shape,shape composed of combined flat portions (e.g. E-shape, F-shape,H-shape, I-shape, K-shape, L-shape, M-shape, N-shape and T-shape) orother desired shapes. An example of the special cross-section is, forinstance, C-shape.

The transverse cross-sectional shape of the conjugate fiber of themolded article (III) can be circular, elliptic or non-circular (e.g.polygonal shape or multi-blade shape). The ratio (volume ratio) of theeasily degradable (co)polyester to the aromatic copolyester can be anarbitrary value, but the ratio is preferably from 5/95 to 75/25, morepreferably from 10/90 to 60/40. If the proportion of the easilydegradable (co)polyester is less than 5% (by volume), it becomesdifficult to have favorable fiber cross section for the conjugate fiberas shown in FIGS. 13 to 24. As a result, it also becomes difficult todivide the fiber-forming segments made of the aromatic copolyester bydissolving the easily degradable (co)polyester. On the other hand, ifthe proportion of the easily degradable (co)polyester is more than 75%(by volume), it also becomes difficult to have a fiber cross-sectionfavorable for the conjugate fiber. Further, since the component to bedissolved overwhelmingly increases, the yield is very poor, thuseconomically disadvantageous.

Examples of the transverse cross-sectional structure of the conjugatefibers of the molded article (III) are shown in FIGS. 13 to 22. In thefigures, oblique line portion 33 is a segment made of the easilydegradable (co)polyester containing the lactic acid component as a maincomponent, and dotted portion 34 is a segment made of the fiber-formingaromatic copolyester containing an aromatic compound as a maincomponent. FIG. 13 shows an instance wherein the aromatic copolyester 34is divided into two portions. FIGS. 14 to 16 show instances of beingconjugated in a radial form wherein the aromatic copolyester 34 isdivided by the easily degradable (co)polyester of a radial shape intothree segments in FIG. 14, four segments in FIG. 15, and eight segmentsin FIG. 16. FIG. 17 shows an instance of being conjugated in amulti-core (or islands-sea) form wherein the aromatic copolyester 34 isdivided into 14 cores (islands) by the matrix (sea) of the easilydegradable (co)polyester 33. FIG. 18 shows an instance of beingconjugated in a petal form wherein the aromatic copolyester 34 isdivided into eight petal-shaped segments by the easily degradable(co)polyester 33. FIG. 19 shows an instance of being conjugated in amulti-islands-sea form. FIG. 20 shows an instance of being conjugated ina mosaic form wherein the aromatic copolyester 34 is divided intosegments in the form of islands and broken pieces of various shape. FIG.21 shows an instance of a multi-parallel type conjugate fiber whereinthe aromatic copolyester 34 is divided into eight thin-layered segments.FIG. 22 shows an instance of a special cross-sectional shape wherein thearomatic copolyester 34 is divided by the keyhole-like easily degradable(co)polyester 33 into a C-shaped segment and a radial core. If thisconjugate fiber is treated with a weak alkali to decompose and removethe easily degradable (co)polyester 33, a hollow fiber excellent inwater absorption property and heat retaining property is obtained. FIG.23 shows an instance of being conjugated in a hollow radial form whereinthe aromatic copolyester 34 is divided by the easily degradable(co)polyester 33 into eight segments wherein numeral 35 is a hollowportion. FIG. 24 is an instance of being conjugated in a core-providedradial form wherein the aromatic copolyester 34 is divided by the easilydegradable (co)polyester 33 into a central core and 8 segments disposedaround the core.

The thickness of the conjugate fiber is usually not less than 0.5 d andnot more than 20 d, preferably not less than 1 d and not more than 10 d.Fibers having a thickness of less than 0.5 d can be made, but theworkability and productivity are poor or the production thereof requiresa special method and is not general.

The thickness of the fiber of the aromatic copolyester portion after thedegradation of the easily degradable (co)polyester is, therefore,usually not more than 1 d, preferably not more than 0.5 d, morepreferably not more than 0.2 d, still more preferably not more than 0.1d, and is not less than 0.01 d. When the thickness of the fiber is notmore than 1 d, the gloss and softness becomes marked based on itsthinness, and properties peculiar to ultra-fine fibers, such as wipingproperty, which are not seen in conventional fibers, appear at and belowabout 0.5 d. This property becomes particularly marked below 0.2 d.

The conjugate fibers of the molded article (III) can be prepared byconducting a multi-component fiber spinning in a manner such as meltspinning, wet spinning, dry spinning or wet-dry spinning, but themulti-component fiber melt spinning method is the best from theviewpoints of good stability in composite structure and good efficiency.

To the melt spinning method are applied a two step method wherein thespinning and the drawing are conducted in separate steps, a spin-drawmethod wherein the spinning and the drawing are conductedsimultaneously, a method for preparing a partially oriented yarn (POY)by conducting the spinning at a high velocity (e.g. 3,000 to 4,000m/min.), a method for preparing a highly oriented fiber at one effort byconducting the spinning at a ultra-high velocity (e.g. not less than5,000 m/min.), a Spun-Bond method, a flash spinning method, and thelike.

For achieving the multi-component fiber melt spinning, it is desirablethat the difference in melt viscosities at the melting point and thespinning temperature between the easily degradable (co)polyester and thearomatic copolyester is not so large. The melting point of poly-L-lacticacid homopolymer drawn for crystallization is about 178° C. The meltingpoint of modified polylactic acids prepared by copolymerization ormixing with a third component lowers, in many cases, with decrease ofthe crystallinity, and finally they become amorphous and the meltingpoint of crystals disappears. However, for smoothly conducting spinning,drawing, production of knit and woven fabrics and processing step, it ispreferable that the easily degradable (co)polyester has a melting pointor softening point of at least 100° C., especially at least 130° C.

On the other hand, the melting point of the aromatic copolyester can beconsiderably changed by changing the composition thereof, but it ispreferable in smoothly conducting the multi-component fiber meltspinning with the easily degradable (co)polyester that the aromaticcopolyester has a melting point or softening point of 100° to 250° C.,especially 130° to 220° C.

Next, the process for preparing molded articles from the copolyesters ofthe present invention is explained below.

In the present invention, the molded articles of biodegradablecopolyesters are prepared by subjecting to a continuous polymerizationin a molten state a mixture of a lactic acid component comprisingL-lactic acid, D-lactic acid and/or their cyclic dimers (lactide) as amain component with (A) a component comprising polyethylene glycolhaving a number average molecular weight of at least 300, (B) analiphatic polyester component or (C) a sulfo group-containingester-forming compound component to produce the biodegradablecopolyesters having an average molecular weight of at least 50,000,leading the resultant directly to a molding machine withoutsolidification and chip formation thereof, and conducting melt molding.

The first feature of the process of the present invention is that themolding is carried out using a polymer, the molecular weight of which ismarkedly raised to a much higher level than that of conventional ones,and the second feature is that the molecular weight is prevented fromlowering in the fiber forming step as much as possible. For thispurpose, in the present invention monomers containing the lactic acidcomponent as a main component are continuously copolymerized in themolten state, and after the polymerization the polymer (biodegradablecopolyester of the present invention) is directly led to a moldingmachine without soldifying and forming it into chips and is melt-molded.

Upon the copolymerization, it is preferable that the equivalent ratio ofhydroxyl group and the carboxyl group is substantially 1, and anantioxidant is added.

The higher the molecular weight of the copolyester to be produced, thebetter the strength of the fibers to be produced. The average molecularweight is usually at least 50,000, especially at least 70,000,preferably at least 80,000, more preferably at least 100,000, still morepreferably at least 120,000.

If the average molecular weight is excessively large, a longpolymerization time is required, so a reverse reaction proceeds to causeincrease of by-products and discoloration or to decrease the fluidity atthe time of melting and the moldability. From such points of view, theaverage molecular weight is at most 500,000, preferably not more than400,000, more preferably not more than 300,000.

The copolyesters used in the process of the present invention containthe above-mentioned components (A) to (C). Since the amounts of them tobe copolymerized and the like are as already explained, the explanationis omitted here.

The copolyesters produced by copolymerization (for example, in case ofthe copolyester (A), the biodegradable copolyester having an averagemolecular weight of at least 50,000, especially at least 70,000,obtained by continuously copolymerizing 99.5 to 85% of L-lactic acid,D-lactic acid and/or their cyclic dimers (lactide) with 0.1 to 15% ofpolyethylene glycol having a number average molecular weight of at least300 in a molten state) are directly introduced to a spinning headwithout solidification and chip formation thereof, subjected to meltspinning, then drawn at least 3 times, and heat-treated to givebiodegradable copolyester molded articles having a fiber strength of atleast 3 g/d with keeping an average molecular weight of at least 50,000,especially at least 70,000.

Of course, a circulation line and a withdrawing apparatus for thepolymer may be provided, as occasion demands, in order to balance therate of polymerization and the spinning velocity. Also, it is preferableto provide a device for removing the monomers between the polymerizationapparatus and the spinning apparatus. For example, the molten polymersent out of the polymerization apparatus by a geared pump is introducedinto the spinning apparatus through an expansion vessel or a thin filmtype evaporation apparatus to once release the pressure of the moltenpolymer, whereby the residual monomers, and low boiling substances andwater produced by decomposition, can be removed to such an extent as notcausing troubles in practical stable manufacturing and quality.

As mentioned above, the copolyester (A) is directly introduced into aspinning machine. The copolyester is required to have an averagemolecular weight of at least 50,000, especially at least 70,000,preferably at least 80,000. More preferably, the average molecularweight is at least 100,000 and the residual monomer content is at most5%, especially the average molecular weight is at least 120,000 and theresidual monomer content is at most 3%.

If the molecular weight is less than 50,000, the spinning and drawingworkability of the fiber is not sufficient, and the fiber strength doesnot easily reach 3 g/d. In case that the molecular weight of the polymeris not less than 80,000, it has a sufficient spinning and drawingworkability, and moreover the fiber strength may reach 4 g/d.

However, if the molecular weight exceeds 500,000, the spinning anddrawing properties are lowered, so it becomes difficult to obtain asufficient production speed. Therefore, the most preferable molecularweight is from 120,000 to 300,000.

A slight amount of monomers remaining in the polymer can be removed bythe above-mentioned method, and a slight amount of still remainingmonomers and the like sublime at the time of spinning out the polymerfrom the outlet of a spinneret. The sublimates are sucked and recoveredby cooling air which serves also to cool the filaments spun out. Therecovered monomers and others are separated, purified and utilized againas the raw materials for the polymerization.

The spinning temperature may be the same as the polymerizationtemperature, or may be changed up and down to some extent in accordancewith the viscosity of the polymer. However, the spinning is usuallycarried out at a temperature within the range between the melting pointof the polymer and a temperature higher than the melting point by atmost about 50° C. Preferably, the spinning temperature is from themelting point of polymer + about 10° C. to the melting point ofpolymer + about 30° C.

The spinnerets may be those used in a usual melt spinning. It is alsopossible to use spinnerets having at most 200 holes for filamentproduction and spinnerets having at least 30,000 holes for stapleproduction. The size of the hole in the spinnerets may be a usuallyadopted size. The shape of the spinnerets is not particularly limited.For instance, any of the spinnerets used at present such as circular,hollow circular and rectangular spinnerets can be used without anylimitation.

The spinning conditions, such as taking-up speed, oiling and optionalinterlacing, are selected within the ranges of usual conditions. Thespinning draft (taking-up speed/spinning-out speed ratio) is usually notless than 30, preferably not less than 40 and not more than 500.

After the spinning, drawing is conducted. The drawing can be conductedby various methods such as one stage drawing-heat treatment and twostage drawing-heat treatment. The drawing temperature is usually from50° to 100° C., preferably from 60° to 90° C., more preferably from 60°to 80° C. In case of successively conducting the second stage drawing,the drawing temperature in the second stage is usually within the rangebetween the drawing temperature in the first stage and the first stagedrawing temperature +20° C. The heat treatment may be suitably conductedin accordance with the objects of the fibers. That is to say, formaintaining a high shrinkability, heat treatment at a lower temperatureis better or no heat treatment may be conducted. Conversely, forlowering the shrinkability of fibers as low as possible to obtain stablefibers, it is better to conduct the heat treatment at temperatures ashigh as possible. Usually, the heat treatment temperature is at least(drawing temperature +20° C.), preferably within the range betweendrawing temperature +20° C. and drawing temperature 50° C., providedthat it is below the melting point of the polylactic acid copolymers.The higher the drawing ratio, the higher the fiber strength. In general,the drawing ratio is at least 2.5 times, preferably 3.0 to 6 times, morepreferably 3.5 to 5 times.

In case of conducting the drawing in two or more stages, it is conductedunder basically the same conditions, but the second stage drawing ratiois usually made lower than the first stage drawing ratio.

The fibers after the drawing have a fiber strength much higher than thatof conventional biodegradable fibers, and the fiber strength is usuallyat least 3 g/d, preferably at least 3.5 g/d, more preferably at least 4g/d, particularly preferably at least 5 g/d.

The degree of crystal orientation of the fibers is fairly high. Thedegree of crystal orientation is determined from the half-value width ofthe wide angle X-ray diffraction. In case of the high strength fibers ofthe present invention, the degree of crystal orientation is usually atleast 70%, preferably at least 75%, more preferably at least 80%.

The fibers after the drawing have a melting point of not less than 110°C. The higher the melting point, the better in point of the heatresistance. Food containers are required to be able to conduct asterilization treatment with boiling water of 100° C. For this reason,it is necessary that the melting point is at least 110° C., and amelting point of not less than 130° C. is particularly preferable.Similarly, the fibers are required to withstand dyeing at 100° C. andbacteria, and from such points of view, it is necessary that the meltingpoint is not less than 110° C., and a melting point of not less than130° C. is particularly preferable. Further, it is preferable towithstand a high degree of sterilization (high pressure steam of 130°C.) and a high pressure dyeing (high pressure water bath of 130° C.),and for these purposes, a melting point of not less than 150° C. ispreferable.

Also, the stability of the fibers increases with increasing the degreeof crystallization, but the biodegradability tends to somewhat lower. Incase of the so obtained fibers, the heat of fusion at the melting pointis usually at least 5.0 cal/g, preferably from 7.0 to 12.0 cal/g, forthe purpose of good dynamic stability and biodegradability of thefibers.

According to the process of the present invention, there can be solved aproblem of deterioration owing to oxidation in a cooling step whichoccurs when taking out a conventional polymerization chip once as asolid polymer by water cooling or air cooling, and a problem ofdeterioration and decrease in molecular weight at the time of drying,for example, a problem that a polymer having a molecular weight of100,000 at the time of polymerization decreases its molecular weight toabout 80,000 after the drying, and further decreases to about 60,000 ifmolten again for spinning, so fibers having a high molecular weight anda high strength are not obtained. Thus, fibers having a high molecularweight and a high strength can be prepared practically andinexpensively.

Also, according to the process of the present invention, there can besolved a problem in lowering of quality of final products (discolorationand production of depolymerization products) and lowering of workabilityencountered when raising the degree of polymerization in order to raisethe molecular weight of the final products.

With respect to concrete examples of use of the thus prepared fibers, anexplanation is given below.

Stockings having an excellent biodegradability are obtained by knittingusing a fiber of the above-mentioned biodegradable copolyester and apolyurethane fiber as main knitting yarns.

The stockings comprehends stockings and pantyhose for men and women, butare particularly those intended for women's use.

The fibers used in the stockings are gray yarn, finished yarn, coveredyarn and the like, and they are used properly depending on parts of thestocking and how to knit.

In case of using for stockings, it is preferable that the lactic acidcomponent is L-form or D-form having an optical purity of at least 90%.If the optical purity is low, the crystallinity of the polymer is low,so the heat resistance and mechanical properties of the polymer aredecreased.

Also, as the polylactic acid-based polymer, there can be usedhomopolymers having an average molecular weight of at least 50,000,preferably at least 80,000, more preferably at least 100,000, especiallyfrom 100,000 to 300,000, but copolyesters are preferable, since if 0.1to 10% of polyethylene glycol having a number average molecular weightof at least 600, preferably 0.5 to 5% of polyethylene glycol having anumber average molecular weight of 2,000 to 20,000, is copolymerizedthereinto, the polymerization procedures, particularly mixing,degassing, liquid sending and the like, become easy and the uniformcopolyesters having an excellent quality are obtained, so the heatfluidity of the polymers is remarkably improved and the spinning anddrawing properties and the yarn properties (particularly strength) arealso improved.

If the average molecular weight is less than 50,000, not only thestrength and elongation are low, but also the workability such asspinning and drawing properties becomes insufficient. Also, if theaverage molecular weight is more than 300,000, the melt viscosity of thepolymers becomes too large, so the spinning temperature must be raisedand the polymers are easy to cause their degradation and deteriorationin the spinning stage.

The fibers to be used, formed from the biodegradable copolyesters, arepreferred to have higher strength and elongation because of causing lesstroubles in a covering step with a urethane yarn and in a knitting stepfor producing stockings. The strength is usually at least 3 g/d,preferably at least 3.5 g/d, more preferably at least 4 g/d. Also, theelongation is usually at least preferably at least 30%, more preferablyat least 35%.

With respect to the fineness of the fibers, the thinner, the softer thefeeling of wearing, but a problem in durability may arise. Therefore,the fineness is usually from 5 to 50 d, preferably from 10 to 30 d. Thedenier of single yarn constituting the fiber is at most 5 d, preferablyat most 3 d, more preferably at most 2 d, and is usually not less than 1d.

The molecular weight of PEG used in stockings is preferably not lessthan 600 in terms of number average molecular weight. In order to obtainthe copolyesters having a high degree of polymerization and a highmelting point, PEG is preferred to have a higher molecular weight, andit is more preferably not less than 1,000, particularly preferably from4,000 to 20,000.

The copolyesters of the present invention have a melting point of atleast 110° C. The higher the melting point, the more preferable in pointof heat resistance. The stockings are exposed usually to a temperatureof not less than 100° C., in certain circumstances at a temperature ofnot less than 120° C., at the time of dyeing. Therefore, preferably themelting point is not less than 130° C.

To the fibers formed from the biodegradable copolyesters may be added adelustering agent such as titanium oxide or magnesium oxide, and variousorganic and inorganic pigments, including carbon black. In particular,the addition of pigments is important in raising a fashion character ofpantyhose. These delustering agents and pigments may be added at thetime of conducting either the polymerization for the biodegradablecopolyesters or the spinning, but it is more preferable to add justbefore the spinning.

Examples of other additives are a heat stabilizer, a light stabilizer, awater repellent, an agent for imparting a hydrophilic property, alubricant and other additives usually employed in fiber manufacturing,and these additives can be added.

As the polyurethane fiber, there can be used urethane fibers usuallyemployed in pantyhose. Polyester type polyurethane fibers which areconvenient for biodegradation, are preferred rather than polyether typepolyurethane fibers.

The fineness of the polyurethane fibers is required to giveconsideration to the stretch back property of articles required forcovered yarns. The fineness is usually from 10 to 30 d and the number offilaments is usually from 1 to 3, but they are not always required tofall within these ranges and more suitable fineness and filament numbershould be used in accordance with the uses and performances.

The polyurethane fibers can be prepared by any of usually employedsolution spinning methods (wet spinning, dry spinning) and melt spinningmethods. However, melt spinnable polyurethanes have a great advantagethat combined filament formation is possible in the spinning stage and astep can be omitted.

A method for producing stockings using the polyurethane fiber and thebiodegradable copolyester fiber may be the same as conventional methodsfor producing stockings from polyurethane fiber and nylon fiber or frompolyurethane fiber and polyester fiber. That is to say, there areadoptable a method wherein the biodegradable copolyester fiber is woundsingle (single covered yarn) or double (double covered yarn) around thepolyurethane fiber as a core component, and other combined methods.

The polyurethane fiber wound with the biodegradable copolyester fiber isknitted up to stockings in a usual manner. For instance, there aremethods for knitting up by using only the covered yarn, or by usingalternately the covered yarn and the biodegradable copolyester fiber.

It is also preferable to reinforce the toe portion and the heel portionby increasing the knitting density or altering the knitting structure.

In the panty portion is used a covered yarn made of the biodegradablecopolyester fiber having a somewhat larger thickness and the urethaneyarn, or a covered yarn in combination with a false twist finished yarnof the biodegradable copolyester fiber. The fineness of thebiodegradable copolyester fiber is usually at most 200 d, preferably atmost 150 d, more preferably at most 100 d, particularly preferably from50 to 80 d. Of course, this yarn is also used in the covered yarn withthe urethane yarn. Also, other fibers such as silk and nylon may be usedin part.

To conduct scouring, dyeing and setting in order to improve the qualityand consumption performances of the articles after the knitting is thesame as in the production of usual pantyhose.

The present invention is explained below based on Examples, but is notlimited to these Examples.

BEST MODE FOR CARRYING OUT THE INVENTION

In the present invention, the average molecular weight of the copolymerscontaining the lactic acid component as a main component indicates aweight average molecular weight of high molecular weight compounds(excepting those having a molecular weight of not more than 500) by GPCanalysis (by calibration based on standard polystyrene samples) of a0.1% chloroform solution of a sample.

Also in the present invention, the melting point of a polymer is a peakvalue of heat absorption for fusion of main crystals, measured (heat-uprate of 10° C./min.) by a differential scanning calorimetry (DSC) methodwith respect to fibers sufficiently oriented and crystallized byspinning, drawing and heat-treating. In case of an amorphous polymer, atemperature at which the melt viscosity is 100,000P is regarded as thesoftening point.

Further, the viscosity (relative viscosity) of a solution of the polymerof the present invention indicates a value measured at 20° C. by anOstwald viscometer with respect to a solution of 1 g of a sampledissolved in 100 ml of a mixed solvent of phenol and tetrachloroethanein a ratio of 6/4 (weight ratio).

Also, the impact strength in the present invention is a value measuredby an Izod method (ASTM D-256a) with respect to a V-notched samplehaving a thickness of 1/2 inch and a width of 1/4 inch. The copolymersof the present invention show an Izod impact strength of preferably notless than 1 kg/cm/cm.

EXAMPLE 1 AND COMPARATIVE EXAMPLES 1 AND 2

L-lactide having 99.8% optical purity sufficiently dried (water contentnot more than 100 ppm) and pre-melted, and PEG (#6000 produced by NipponOil & Fats Co., Ltd.) having a number average molecular weight of 8,200,which was dried and melted similarly and to which 0.1% of Irganox 1010,i.e. a hindered phenol antioxidant produced by Ciba Geigy Corp., wasadded, were supplied to the raw material feed part of a twin-screwkneader in a ratio (weight ratio) of 98/2. Simultaneously, 0.3% of tindioctylate was added as a polymerization catalyst based on the lactide.

The twin-screw kneader is one shown in FIGS. 1 and 2, and comprisesplural feed screws of 30 mm diameter and plural 7 mm thick twoblade-shaped agitating elements. The feed screws were disposed in theraw material feed part and two vent hole parts, and the agitatingelements were disposed in the other parts.

The section of the cylinder was elliptic and was constricted around itscenter portion. The temperature was set at 190° C. A nitrogen gas wassupplied through the first vent hole and exhausted through the secondvent hole. Two rotation shafts were rotated in the same direction, andthe number of rotations was 60/min.

The polymer discharged from the twin-screw kneader was fed to a second40 mm diameter twin-screw kneader directly connected thereto andprovided with two vent holes. The cylinder temperature was 190° C. Therotation was in the same direction, and the number of rotations was40/min. A small amount of a nitrogen gas was supplied through the firstvent hole, and the second vent hole was connected to a vacuum pump tokeep a vacuum degree at about 0.5 Torr, while the above-mentionedantioxidant was added in an amount of 0.1% based on the polymer. Thepolymer discharged from the second twin-screw kneader was fed by ageared pump, filtered with a 20 μm filter, extruded through a 2 mmdiameter nozzle, cooled with water to solidify and cut to obtain chipsP1. The average residence (reaction) time of the polymer in the firsttwin-screw kneader was 5.5 minutes, and the residence time in the secondkneader was 16 minutes. The total average polymerization time was 21.5minutes.

There was no discoloration on the P1, and the transparency wasexcellent.

For comparison, 0.3% of tin dioctylate was added to 15 kg of lactide. Ina 100 l polymerization vessel with a usual uniaxial agitator, themixture was polymerized under normal pressure at 210° C. for the firstone hour in a nitrogen stream, and then the pressure was reducedgradually over 30 minutes, followed by 60 minutes polymerization at 0.5Torr. Since the torque of the agitator reached nearly a constant value,the pressure was turned back to normal pressure, followed by pressureapplication, extrusion, cooling and cutting to give chips P2 of a PLLAhomopolymer.

P2 was tinged with light brown, and opaque portions and remarkablycolored portions were observed in part.

Chips P3 were prepared in the same manner as in P2 except that 2% of PEGhaving a number average molecular weight of 8,200 was added to 98% oflactide and they were polymerized.

P3 was tinged with light brown, and there were opaque portions andremarkably colored portions.

P1 was melted at 240° C. by a screw extruder, spun through an orifice of245° C. with 0.2 mm diameter holes, and cooled in air, followed byoiling and winding at a speed of 800 m/min, to give an un-drawn yarnUY1. UY1 was drawn at 70° C. in a drawing ratio of 3.3, and thenheat-treated at 150° C. under a tension and wound at a speed of 600m/min to give a drawn yarn DY1 of 75d/18f (filament).

Drawn yarns DY2 and DY3 were prepared with the use of P2 and P3 in thesame manner as in DY1 except that the drawing was conducted in a drawingratio as high as possible.

The workability in spinning and drawing of DY1, DY2 and DY3 and thecharacteristics of them are shown in Table 1.

Also DY1, DY2 and DY3 were immersed in an activated sludge, and 6 monthslater the strength of them was measured. As a result of the measurement,the strength of them was all not more than 1/3 of the initial strength,and it was found that DY1, DY2 and DY3 have a good biodegradability.

                                      TABLE 1                                     __________________________________________________________________________                       Example  Comparative                                                                          Comparative                                                   No. 1    Example 1                                                                            Example 2                                  __________________________________________________________________________    Yarn               DY1      DY2    DY3                                        Polymer composition                                                                              Copolyester                                                                            PLLA   Copolyester                                                   containing 2%                                                                          homopolymer                                                                          containing 2%                                                 PEG 8200        PEG 8200                                   Viscosity of polymer solution                                                                    2.8      1.8    1.7                                        Average molecular weight of polymer                                                              82000    36000  31000                                      Melting point (°C.)                                                                       171      178    170                                        Spinning workability                                                                             good,    bad,   bad,                                                          no yarn breaking                                                                       yarn breaking                                                                        frequent                                                               observed                                                                             yarn breaking                              Drawing ratio      3.3      2.8    2.8                                        Drawing workability                                                                              good     bad    bad                                                           no yarn breaking                                                                       frequent                                                                             frequent                                                               yarn breaking                                                                        yarn breaking                              Strength (g/d)     2.8      1.7    1.5                                        Elongation (%)     28       16     17                                         Young's modulus (g/d)                                                                            5.10     3.47   3.44                                       __________________________________________________________________________

It is found from Table 1 that as compared with DY2 and DY3 prepared bythe conventional process, DY1 prepared from the copolymer of the presentinvention has a very excellent workability in spinning and drawing andan excellent toughness (strength and elongation).

Similarly, V-notched samples for an impact test were prepared with theuse of P1, P2 and P3 by means of an injection molding machine of 175° C.

With the use of respective chips, the polymers were melted at 180° C. bya screw extruder, extruded from a T-shaped spinneret of the sametemperature, cooled and wound to prepare a film. Then the film wasstretched 3.8 times at 60° C. and heat-set at 120° C. to prepare astretched film having a thickness of 58 μm. The impact strength of thesamples obtained from the respective chips and the tensile strength andelongation of the films were measured. The results are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                                  Example  Comparative                                                                              Comparative                                               No. 1    Example 1  Example 2                                       ______________________________________                                        Chip        P1         P2         P3                                          Impact strength                                                                           1.8        0.6        0.8                                         (kg · cm/cm)                                                         Film strength                                                                             30.7       19.4       18.8                                        (kg/mm.sup.2)                                                                 Film elongation (%)                                                                       22         14         18                                          ______________________________________                                    

EXAMPLE 2

PEG having various molecular weights (number average molecular weights)were copolymerized with lactide in various copolymerization ratios innearly the same manner as in Example 1.

The proportion of PEG in copolymerization, and the average molecularweight, polymerization conversion and melting point of the obtainedcopolymers are shown in Table 3.

The polymerization conversion is the weight percentage of a highmolecular weight component having a molecular weight exceeding 500, thatis to say, one excluding a low molecular weight component such as aresidual monomer in the polymer. The melting point of the polymer wasmeasured by a DSC method. There is a case where it is somewhat lower (byabout 2° to about 7° C.) than the melting point of a drawn and orientedfiber, but they are nearly approximate in values. The proportioncopolymerization shown in Table 3 indicates the composition of rawmaterials charged. The PEG content in the obtained high molecular weightcomponent is obtained, for example, if the polymerization conversion is90%, by multiplying the PEG proportion in the raw material compositionby about 1.1.

                                      TABLE 3                                     __________________________________________________________________________    Number average                                                                molecular         Proportion of PEG in copolymerization (%)                   weight of PEG     0.1                                                                              0.3                                                                              0.5                                                                              1  3  6  8  10 12                                  __________________________________________________________________________     600     Mw (*1) × 10.sup.-3                                                              71 65 51 50 22 -- -- -- --                                           Conversion (%)                                                                         82 86 81 80 71 -- -- -- --                                           Tm (*2) (°C.)                                                                   166                                                                              164                                                                              166                                                                              162                                                                              160                                                                              -- -- -- --                                  1000     Mw × 10.sup.-3                                                                   85 82 79 55 51 26 -- -- --                                           Conversion (%)                                                                         89 88 85 83 83 70 -- -- --                                           Tm (°C.)                                                                        167                                                                              166                                                                              168                                                                              163                                                                              165                                                                              165                                                                              -- -- --                                  3500     Mw × 10.sup.-3                                                                   91 94 82 88 80 55 30 -- --                                           Conversion (%)                                                                         88 85 85 80 81 86 62 -- --                                           Tm (°C.)                                                                        168                                                                              166                                                                              166                                                                              167                                                                              167                                                                              167                                                                              166                                                                              -- --                                  8200     Mw × 10.sup.-3                                                                   101                                                                              103                                                                              100                                                                              83 103                                                                              90 51 33 --                                           Conversion (%)                                                                         91 90 91 88 89 86 82 75 --                                           Tm (°C.)                                                                        170                                                                              169                                                                              168                                                                              168                                                                              167                                                                              167                                                                              167                                                                              162                                                                              --                                  10500    Mw × 10.sup.-3                                                                   92 95 90 90 88 90 82 50 42                                           Conversion (%)                                                                         90 90 91 89 90 87 88 77 67                                           Tm (°C.)                                                                        170                                                                              169                                                                              169                                                                              170                                                                              167                                                                              166                                                                              169                                                                              160                                                                              165                                 19000    Mw × 10.sup.-3                                                                   90 92 99 89 91 90 85 81 55                                           Conversion (%)                                                                         89 87 80 88 90 87 85 80 75                                           Tm (°C.)                                                                        170                                                                              170                                                                              169                                                                              166                                                                              165                                                                              170                                                                              169                                                                              169                                                                              168                                 __________________________________________________________________________     (Note *1)                                                                     Mw: Weight average molecular weight of polymer (excepting low molecular       weight compound) (same as the average molecular weight in the present         invention)                                                                    (Note *2)                                                                     Tm: Melting point of polymer (chip)                                      

It is found from Table 3 that there is a tendency that the smaller themolecular weight of PEG is, the more the degree of polymerization ishard to increase. In case of PEG having a number average molecularweight of 600, it is difficult to obtain a copolymer having an averagemolecular weight of not less than 50,000 when the copolymerizationproportion is not less than 3%. Similarly in case of PEG having numberaverage molecular weights of 1,000, 3,500, 8,200 and 10,500, it isdifficult to obtain high molecular weight copolymers when thecopolymerization proportions are not less than 6%, 8%, 10% and 12%,respectively.

Fibers obtained from the copolymers containing 1% of PEG having a numberaverage molecular weight of 1,000, 3,500, 8,200 or 10,500 were immersedin activated sludge for six months, and the strength thereof wasmeasured. The strength was all not more than 1/2, thus showing a goodbiodegradability.

EXAMPLE 3

PEG having a number average molecular weight of 1,000 was copolymerizedwith lactide at a copolymerization proportions of 3% and 6% respectivelyin the same manner as in Example 2 except that 0.44% and 0.9% (equimolarwith PEG component) phthalic anhydride were charged and reactedrespectively based on the polymerization system through the first venthole of the second twin-screw kneader.

The average molecular weight of the obtained copolymers is as shown inTable 4, and an effect enhancing the degree of polymerization based on abalance in end groups is recognized.

The fibers prepared from the obtained copolymers were allowed to standin the ground for six months, and the appearance thereof was observed.There were observed voids in part and changes such as swelling andtearing. The strength of the fibers immersed in activated sludge was notmore than 1/2, thus showing a good biodegradability.

                  TABLE 4                                                         ______________________________________                                                                Proportion of PEG in                                  Polymerization          copolymerization (%)                                  manner      Measured value                                                                            3         6                                           ______________________________________                                        Addition of Mw × 10.sup.-3                                                                      82        65                                          phthalic anhydride                                                                        Conversion (%)                                                                            83        77                                                      Tm (°C.)                                                                           165       163                                         No use of   Mw × 10.sup.-3                                                                      51        26                                          phthalic anhydride                                                                        Conversion (%)                                                                            83        70                                                      Tm (°C.)                                                                           165       165                                         ______________________________________                                    

EXAMPLE 4

L-lactide having an optical purity of 99.8%, dried sufficiently (watercontent not more than 100 ppm) and pre-melted, and a polyethyleneadipate having a weight average molecular weight of 3,000, to which 0.1%of Irganox 1010 made by Ciba Geigy Corp., i.e. a hindered phenolantioxidant, were supplied in a polymerization ratio of 98/2 to the rawmaterial feed part of a twin-screw kneader. At the same time, a tindioctylate was added, as the polymerization catalyst, in an amount of0.3% based on the lactide.

The twin-screw kneader is one shown in FIGS. 2 and 3, and comprisesplural 30 mm diameter feed screws and plural 7 mm thick two blade-shapedagitating elements. The feed screws were disposed in the raw materialfeed part and the two vent hole parts, and the agitation elements weredisposed in the other parts. The section of the cylinder was ellipticand constricted around its center portion. The temperature was set at192° C. A nitrogen gas was supplied through the first vent hole andexhausted through the second vent hole. Two rotation shafts were rotatedin the same direction, and the number of rotations was 50/min.

The polymer discharged from the twin-screw kneader was then supplied toa 30 mm diameter second twin-screw kneader directly connected theretoand provided with two vent holes. The cylinder temperature was 185° C.The rotation was in the same direction, and the number of rotations was40/min. A nitrogen gas was supplied through the first vent hole, and thesecond vent hole was connected to a vacuum pump. The vacuum degree waskept at about 10 Torr, and the above-mentioned antioxidant was added inan amount of 0.1% based on the polymer. The polymer discharged from thesecond twin-screw kneader was pressure-sent with a gear pump, filteredwith a 20 μm filter, extruded through a 3 mm diameter nozzle, cooledwith water to solidify, and cut to obtain chips P4. The averageresidence (reaction) time of the polymer in the first twin-screw kneaderwas six minutes, and the residence time in the second twin-screw kneaderwas eight minutes. The total average polymerization time was 14 minutes.P4 had no discoloration and was excellent in transparency.

P4 was melted by a 210° C. screw extruder, spun through an orifice of200° C. having 0.2 mm diameter holes, and cooled in air, followed byoiling and winding at a speed of 1,000 m/min, to give an un-drawn yarnUY4. UY4 was drawn at 70° C. in a drawing ratio of 3.3, heat-treatedunder a tension at 115° C., and wound at a speed of 800 m/min to give adrawn yarn DY4 of 150 d/48 f.

Spinning and drawing were carried out without yarn breaking, thus theworkability was excellent. Physical properties of the drawn yarn werestrength of 3.6 g/d, elongation of 35% and Young's modulus of 670kg/mm², and the transparency thereof was excellent.

The strength of DY4 after immersed in activated sludge for six monthswas not more than 1/4, thus showing a good biodegradability.

EXAMPLE 5

Aliphatic polyesters having various molecular weights were copolymerizedwith lactides in various ratios in nearly the same manner as in Example4. The proportion of aliphatic polyester in copolymerization conversion,and the average molecular weight, polymerization conversion and meltingpoint of the obtained copolymers are shown in Table 5. Thepolymerization conversion is the weight percentage of a high molecularweight component having a molecular weight exceeding 500, that is tosay, one excluding a low molecular weight component such as a residualmonomer in the polymer. The melting point of the polymer was measuredwith the use of the obtained chips by the DSC method. Though there is acase where the melting point is somewhat lower (about 2° to about 7° C.)than that of the drawn and oriented fiber, they are nearly approximatevalues. The proportion in copolymerization in the Table indicates thecompositions of raw materials charged.

                                      TABLE 5                                     __________________________________________________________________________    Sample                                                                            Polyester*.sup.1                                                                           Produced polymer                                             No. n m p Amount (%)                                                                           Tm (°C.)                                                                    η rel                                                                        Spinning property                                    __________________________________________________________________________     1  2 2 20                                                                              0      173  2.5                                                                              yarn breaking during spinning, whitening                                      during drawing                                        2  ↑                                                                         ↑                                                                         ↑                                                                         0.5    173  3.4                                                                              good                                                  3  ↑                                                                         ↑                                                                         ↑                                                                         3      170  3.1                                                                              good                                                  4  ↑                                                                         ↑                                                                         ↑                                                                         5      165  2.9                                                                              nearly good                                           5  ↑                                                                         ↑                                                                         ↑                                                                         10     160  2.7                                                                              nearly good                                           6  ↑                                                                         ↑                                                                         ↑                                                                         15     150  2.5                                                                              yarn breaking sometimes during spinning               7  4 2 40                                                                              0.5    172  3.2                                                                              good                                                  8  ↑                                                                         ↑                                                                         ↑                                                                         3      170  3.6                                                                              good                                                  9  ↑                                                                         ↑                                                                         ↑                                                                         5      163  3.2                                                                              good                                                 10  ↑                                                                         ↑                                                                         ↑                                                                         10     157  3.0                                                                              good                                                 11  ↑                                                                         ↑                                                                         ↑                                                                         15     150  2.7                                                                              yarn breaking sometimes during spinning              12  4 4 20                                                                              0.5    173  3.5                                                                              good                                                 13  ↑                                                                         ↑                                                                         ↑                                                                         3      171  3.7                                                                              good                                                 14  ↑                                                                         ↑                                                                         ↑                                                                         5      168  3.4                                                                              good                                                 15  ↑                                                                         ↑                                                                         ↑                                                                         10     160  3.2                                                                              good                                                 16  ↑                                                                         ↑                                                                         ↑                                                                         15     151  2.9                                                                              yarn breaking sometimes during spinning              17  6 4 70                                                                              0.5    173  2.9                                                                              yarn breaking sometimes during spinning              18  ↑                                                                         ↑                                                                         ↑                                                                         3      171  3.2                                                                              nearly good                                          19  ↑                                                                         ↑                                                                         ↑                                                                         5      169  3.3                                                                              nearly good                                          20  ↑                                                                         ↑                                                                         ↑                                                                         10     165  2.8                                                                              yarn breaking sometimes during spinning              21  ↑                                                                         ↑                                                                         ↑                                                                         15     148  2.4                                                                              yarn breaking sometimes during                       __________________________________________________________________________                             spinning                                              (Note *.sup.1)                                                                H[O(CH.sub.2).sub.n OOC(CH.sub.2).sub.m COO].sub.p H                     

EXAMPLE 6 AND COMPARATIVE EXAMPLE 3

In the following Example, a strength deterioration test of fibers wasconducted in the manner mentioned below.

Continuous filaments of 150 d/48 f (single filament 3.1 d) were used asa sample fiber, and wound and fixed under a tension (tension of about 20mg/d) on a 10 cm wide rectangular frame made by bending a 6 mm diameterstainless steel bar. A sample fiber to be compared was wound 1 cm apartfrom the mentioned sample in the same manner. The stainless steel framewith the samples (yarns) wound thereon was embedded horizontally in thefertile neutral soil (pH 6.5 to 7.0) 10 cm deep from the ground under avictoria lawn for agriculture. Attention was paid so that the soil didnot become excessively dry and wet (shaded area where grasses aregrowing and in the state that the surface of the ground is always wet).The temperature was kept within the range of 25°±5° C.

The samples were taken out every specified period, for instance, everyone week or every one month, and after washing with water and airdrying, three filaments were sampled from each of the samples. Thetensile test was conducted with respect to the filament. The length ofthe test specimen was 5 cm and the rate of tension was 5 cm/min. Thestrength at breaking was measured, and the average value of tenmeasurements was assumed to be a central value. The temperature of atesting room for the tensile test was 20° C., and the humidity was 65%RH.

From a curve on the relationship between the embedded period and thetensile strength at breaking, the time period until the strengthdecreases to 1/2 of the initial strength (not deteriorated), wasobtained as the half-life. It is shown that the smaller the half-lifeis, the faster the deterioration (degradation) speed is.

Bishydroxyethyl sodium sulfoisophthalate, bishydroxyethyl isophthalateand bishydroxyethyl adipate were mixed in a molar ratio of2.10/1.00/1.00, and reacted at 260° C. under normal pressure for onehour. The pressure was then reduced gradually over 15 minutes to adegree of vacuum of 0.1 Torr and was kept for 17 minutes to give aprepolymer PP1. The weight average molecular weight of PP1 was about9,000. The melting point thereof was unable to determine because of lowcrystallinity. The content of the sulfoisophthalic acid component wasabout 51%.

L-lactide was melt-mixed with PP1 in an amount of 18 parts per 1 part ofPP1, and 0.3% of tin dioctylate was added as a polymerization catalyst.The mixture was polymerized at 190° C. for 35 minutes with agitating bymeans of a twin-screw kneader, extruded through a 2 mm diameter nozzle,cooled with water and then cut to obtain chips C1. After centrifugallydehydrated, C1 was vacuum-dried at 80° C. for 48 hours under not morethan 0.1 Torr to remove water and the residual monomer (lactide) to givea copolymer P5.

P5 had an average molecular weight of 155,000, melting point of 173° C.and a content (copolymerization proportion) of the sulfoisophthalic acidcomponent of 3%.

For comparison purpose, L-lactide was polymerized alone using 0.3% oftin dioctylate in the same manner as in P5 and was formed into chips togive a polylactic acid (homopolymer) P6. The average molecular weight ofP6 was 62,000, and the melting point was 175° C.

P5 was melted at 200° C. by a screw extruder, spun through an orifice of190° C. with 0.2 mm diameter holes, and cooled in air, followed byoiling and winding at a speed of 800 mm/min to give an un-drawn yarnUY5. UY5 was drawn at 70° C. in a ratio of 4.2, and then heat-treated at120° C. under a tension to give a drawn yarn DY5 of 150 d/48 f. Thestrength of DY5 was 4.4 g/d, and the elongation was 29.3%.

Also the drawn yarn DY6 was prepared by spinning P6 at 195° C., anddrawing and heat-treating in the same manner as in P5. The strength ofDY6 was 3.2 g/d, and the elongation was 25.6%.

DY5 and DY6 were embedded in soil to carry out a deterioration test. Asa result, the half-life of the strength deterioration of DY5 obtainedfrom the copolymer of the present invention was 2.1 months. In contrast,the half-life of DY6 (Comparative Example 3) made of the un-modifiedpolylactic acid was 7.6 months. The degradation speed of DY5 in which 3%sulfoisophthalic acid component was copolymerized, was about 3.6 timesthat of the un-modified DY6.

A dyeing solution was prepared in a usual manner using a basic dyeKayacrl Blue 2RL-ED 5.0% owf, and a circular-knitted fabric knitted withDY5 yarn was dyed at a bath ratio of 50 by heating up the solution from25° to 95° C. over 30 minutes and further heating at 95° C. for 30minutes. The percentage of exhaustion of the dye was 94.7%, and the yarnwas vividly dyed. After washing with water and drying, the colorfastness after cleaning was measured. Both the change in color and thesolution contamination were in the grade 4 to 5, thus the yarn had asufficient fastness.

For comparison purpose, the dyeing with the basic dye was conducted inthe same manner by using DY6. The percentage of dye exhaustion was only10.5%, so the dyed DY6 was merely in such a state as being contaminated.

Then a dyeing solution was prepared in a usual manner using a dispersedye, Miketon Polyester Blue 2.5% owf, and dyeing was carried out at abath ratio of 50 by heating up the solution from 25° C. to 95° C. over30 minutes and further heating at 95° C. for 30 minutes. The percentageof dye absorption was 25.0%, and the dyeing color was light. The changein color after cleaning was in the grade 1 to 2, and the color fastnesswas poor.

Reference Examples 1 to 3

Poly-L-lactic acid Was prepared by melt-polymerization of an L-lactideas a raw material which was synthesized from L-lactic acid, andpoly-D/L-lactic acid copolymers were prepared by copolymerizing L-lacticacid and D-lactic acid in a predetermined ratio. Melt-adhesivepolylactic acid conjugate fibers of 3 d was prepared by suitablyselecting polylactic acids having melting points as shown in Table 6 asa polymer (a) and a polymer (b), from the obtained poly-L-lactic acidand various kinds of poly-D/L-lactic acid copolymers, and spinning aconjugate fiber of a parallel type (side-by-side type, the same shape asin FIG. 13) comprising the polymer (a) and the polymer (b) in a ratio of4/1, followed by drawing and heat-treating.

These conjugate fibers were formed into cut fibers and then crimped, andtherefrom non-woven fabrics were prepared and evaluated. Binding of thenon-woven fabrics was conducted by heat-embossing. The embossingtemperature was suitably set in the range lower than the melting pointsof the polymer (a) as shown in Table 6. The results are shown in Table6.

The "tensile strength" in Table 6 are values measured by deforming 50 mmwide strip-like test specimens at a rate of extension of 200%/min. Thevalues in the table are shown by the range of actually measured valuesof ten specimens.

The obtained non-woven fabrics were embedded in the soil mentionedbefore (Example 6) for six months, and the change in shape was observed.There was observed cracking and the like on the fibers, and the tensilestrength was at most 1 kg. Thus biodegradability was confirmed.

Comparative Reference Examples 1 and 2

Polylactic acid conjugate fibers were prepared in the same manner as inReference Example 1 except that polylactic acid polymers, of whichdifference in the melting point is less than 10° C., were selected asthe polymers (a) and (b). Then the non-woven fabrics were prepared andevaluated. The results are shown in Table 6.

From Table 6 it is seen that the heat embossing effect is small and theobtained non-woven fabrics are inferior in physical properties.

                                      TABLE 6                                     __________________________________________________________________________                                    Comparative                                                                          Comparative                                          Reference                                                                           Reference                                                                           Reference                                                                           Reference                                                                            Reference                              Items         Example 1                                                                           Example 2                                                                           Example 3                                                                           Example 1                                                                            Example 2                              __________________________________________________________________________    Polymer (a)                                                                   Melting point (°C.)                                                                  170   178   130   175    100                                    Proportion of D-lactic acid                                                                 1     0     5     0      10                                     (mole %)                                                                      Polymer (b)                                                                   Melting point (°C.)                                                                  130   ND*.sup.1                                                                           ND    168    95*.sup.3                              Proportion of D-lactic acid                                                                 5     15    15    1      12                                     (mole %)                                                                      Embossing temperature (°C.)                                                          150   100   70    172    97                                     Tensile strength (kg)                                                                       4 to 9                                                                              3 to 8                                                                              5 to 11                                                                             1 to 5 not more                                                                      than 1                                 Appearance of non-woven                                                                     good  good  surface                                                                             fuzz   wrinkle,                               fabric                    wrinkle      fuzz                                   Weight per square meter                                                                     43    45    52    49     46                                     of non-woven fabric (g/m.sup.2)                                               Polymer (a)/(b) ratio                                                                       50/50 60/40 70/30 50/50  50/50                                  Over-all estimation*.sup.2                                                                  ⊚                                                                    ⊚                                                                    ◯-⊚                                                      Δ                                                                              Δ                                __________________________________________________________________________     (Notes)                                                                       *.sup.1 ND: Amorphous and having no melting point                             *.sup.2 ⊚: Very excellent, ◯: Excellent,           Δ: Inferior                                                             *.sup.3 Showing somewhat vague melting point                             

Reference Examples 4 to 6

The same polylactic acid polymers as in Reference Examples 1 to 3 wereused as polymers (a) and (b), and conjugate fibers were prepared to havea transverse cross sectional structure as shown in FIG. 5 instead of theparallel type structure, thus giving melt-adhesive core-sheath conjugatefibers (3 d) including a core made of the polymer (a) having a highermelting point and a sheath made of the polymer (b) having a lowermelting point in a polymers (a)/(b) ratio of 2/1. Subsequently non-wovenfabrics were prepared in the same manner as in Reference Example 1, andevaluated. The results are shown in Table 7.

Comparative Reference Examples 3 and 4

The same polylactic acid polymers as in Comparative Reference Examples 1and 2 were used as polymers (a) and (b), and conjugate fibers wereprepared, to have a transverse cross sectional structure of a coresheath type instead of the parallel type structure, thus givingcore-sheath conjugate fibers including a core made of the polymer (a)having a higher melting point and a sheath made of the polymer (b)having a lower melting point. Subsequently the non-woven fabrics wereprepared in the same manner as in Reference Example 1, and evaluated.The results are shown in Table 7.

                                      TABLE 7                                     __________________________________________________________________________                                    Comparative                                                                          Comparative                                          Reference                                                                           Reference                                                                           Reference                                                                           Reference                                                                            Reference                              Items         Example 4                                                                           Example 5                                                                           Example 6                                                                           Example 3                                                                            Example 4                              __________________________________________________________________________    Melting point of                                                                            170   178   130   175    100                                    polymer (a) (°C.)                                                      Melting point of                                                                            130   ND    ND    168    95                                     polymer (b) (°C.)                                                      Embossing temperature (°C.)                                                          150   100   80    172    97                                     Tensile strength (kg)                                                                       5 to 8                                                                              4 to 6                                                                              3 to 8                                                                              not more                                                                             not more                                                               than 1 than 1                                 Appearance of non-woven                                                                     good  good  good  fuzz   wrinkle                                fabric                                                                        Weight per square meter                                                                     50    45    49    47     53                                     of non-woven fabric (g/cm.sup.2)                                              Polymer (a)/(b) ratio                                                                       60/40 60/40 60/40 60/40  50/50                                  Over-all estimation                                                                         ⊚                                                                    ⊚                                                                    ⊚                                                                    Δ                                                                              Δ                                __________________________________________________________________________

EXAMPLES 7 AND 8 AND REFERENCE EXAMPLES 7 AND 9

L-lactide was copolymerized with a compound having polyfunctional groups(glycerol (GLC), polyethylene glycol (PEG having a number averagemolecular weight of 8,200)) or DL-lactide in a proportion as shown inTable 8 to give various polylactic acid polymers having differentmelting points. From the obtained polylactic acid polymers were suitablyselected those having the melting points as shown in Table 8 as thepolymers (a) and (b), and conjugate fibers (3 d) having a core-sheathtype or side-by-side type (same shape as in FIG. 13) transverse crosssectional structure and a polymer (a) /polymer (b) ratio of 4/1 weremelt-spun. The obtained conjugate fibers were melt-adhesive polylacticacid-based fibers. Subsequently non-woven fabrics were prepared in thesame manner as in Reference Example 1, and evaluated. The results areshown in Table 8.

                                      TABLE 8                                     __________________________________________________________________________                  Reference                                                                           Reference         Reference                               Items         Example 7                                                                           Example 8                                                                           Example 7                                                                           Example 8                                                                           Example 9                               __________________________________________________________________________    Polymer (a)                                                                   Melting point (°C.)                                                                  173   172   169   167   177                                     Proportion of comonomer                                                                     GLC   GLC   PEG   PEG   none                                    (%)           1     2     1     3     0                                       Polymer (b)                                                                   Melting point (°C.)                                                                  128   100*  100*  150   167                                     Proportion of comonomer                                                                     DL-lactide                                                                          DL-lactide                                                                          DL-lactide                                                                          DL-lactide                                                                          PEG                                     (%)           10    20    20    4     3                                       Kind of composite fiber                                                                     core-sheath                                                                         core-sheath                                                                         parallel                                                                            parallel                                                                            core-sheath                                           type  type  type  type  type                                    Embossing temperature (°C.)                                                          140   110   100   160   170                                     Tensile strength (kg)                                                                       5 to 8                                                                              5 to 9                                                                              4 to 8                                                                              2 to 5                                                                              5 to 10                                 Appearance of non-woven                                                                     good  good  good  good  good                                    fabric                                                                        Weight per square meter                                                                     44    50    47    51    46                                      of non-woven fabric (g/cm.sup.2)                                              Polymer (a)/(b) ratio                                                                       60/40 50/50 50/50 40/60 30/70                                   Over-all estimation                                                                         ⊚                                                                    ⊚                                                                    ◯-⊚                                                      ◯-⊚                                                      ⊚                        __________________________________________________________________________     (Notes)                                                                       *Showing somewhat vague melting point                                    

Reference Examples 10 to 13

L-lactide was copolymerized with glycerol (GLC), DL-lactide or PEG(number average molecular weight 8,200) in the ratio shown in Table 9 togive polymers (a) and (b) having the melting points shown in Table 9.Core-sheath type composite filament yarns comprising the polymers (a)and (b) were then prepared. The obtained core-sheath composite filamentyarns were melt-adhesive polylactic acid fibers having properties asshown in Table 9. The obtained melt-adhesive polylactic acid fibers werewoven in a low density plain gauze, and then passed through heatcalender rolls of 120° C. Thus a plain gauze well secured by fusionwhich has a 0.1 to 5 mm mesh spacing was obtained, and evaluated. Theresults are as shown in Table 9. The plain gauze was very suitable asfood packaging materials such as tea bags.

When the obtained plain gauze was immersed in activated sludge for 6months, the strength against mesh slippage was not more than 0.1 kg andthe strength of the fiber itself became not more than 1/2. Thus a goodbiodegradability was observed.

The "strength against mesh slippage" in Table 9 indicates a lower limitstrength reaching separation of warp and weft when the plain gauzehaving a 0.2 mm mesh spacing was cut at an angle of nearly 45° to thewarp and weft into strip-like 5 cm wide samples and deformed by means ofa tension tester.

Comparative Reference Example 5

A core-sheath type conjugate fiber having properties as shown in Table 9was prepared by using the same polylactic acid polymers as used inComparative Reference Example 3, as the polymers (a) and (b).Subsequently a plain gauze was prepared in the same manner as inReference Examples 10 to 13, and evaluated. The results are as shown inTable 9. The obtained plain gauze was one not suitable for foodpackaging materials such as tea bags.

                                      TABLE 9                                     __________________________________________________________________________                                         Comparative                                           Reference                                                                           Reference                                                                           Reference                                                                           Reference                                                                           Reference                                Items        Example 10                                                                          Example 11                                                                          Example 12                                                                          Example 13                                                                          Example 5                                __________________________________________________________________________    Polymer (a)                                                                   Melting point (°C.)                                                                 173   170   178   177   175                                      Proportion of comonomer                                                                    GLC   GLC   --    --    --                                       (%)          1     3     --    --    --                                       Polymer (b)                                                                   Melting point (°C.)                                                                 128   130   ND*.sup.1                                                                           167   168                                      Proportion of comonomer                                                                    DL-lactide                                                                          DL-lactide                                                                          DL-lactide                                                                          PEG   DL-lactide                               (%)          10    8     24    5     2                                        Polymer (a)/(b) ratio                                                                      60/40 70/30 50/50 40/60 60/40                                    Fineness (d) 24    36    75    24    36                                       Yarn strength (g/d)                                                                        3 to 5                                                                              4 to 6                                                                              3 to 4                                                                              3 to 5                                                                              4 to 6                                   Elongation (%)                                                                             35 to 50                                                                            35 to 60                                                                            33 to 45                                                                            30 to 60                                                                            25 to 60                                 Strength against                                                                           not less                                                                            not less                                                                            1 to 1.8                                                                            0.5 to 1                                                                            not more                                 mesh slippage (kg)                                                                         than 3                                                                              than 3            than 0.1                                 Performance as tea bag*.sup.2                                                              ⊚                                                                    ⊚                                                                    ⊚                                                                    ◯-⊚                                                      Δ                                  __________________________________________________________________________     (Notes)                                                                       *.sup.1 ND: Amorphous and having no melting point                             *.sup.2 ⊚: Very excellent, ◯: Excellent,           Δ: Inferior                                                        

Reference Examples 14 and 15 and Comparative Reference Examples 6 and 7

Sufficiently dried L-lactide having an optical purity of not less than99.9% was polymerized, by using a twin-screw kneader, with agitating at190° C. for 35 minutes in the presence of 0.3% of tin dioctylate as thepolymerization catalyst, 0.1% of Irganox 1010 made by Ciba Geigy Corp.as the antioxidant, and, as a fluidity modifying and water repellentagent, 0.3% of magnesium stearate and 0.5% of polyethylene oxide (acidnumber 15) having a molecular weight of 4,000. After the polymerization,the obtained polymer was extruded through a 3 mm diameter nozzle, cooledwith water and cut into chips. The obtained chips, after centrifugallydehydrated, were dried at 90° C. for 48 hours at a vacuum degree of notmore than 0.1 Torr with a vacuum dryer to remove residual lactides. Thusthe polylactic acid P7 having an average molecular weight of 162,000 andan optical purity of not less than 99.9% was obtained.

The polylactic acid copolymer P8 having an average molecular weight of156,000 and an L/D of 95/5 was obtained in nearly the same manner as inP7 except that the mixture of 95 parts of L-lactide and 5 parts ofD-lactide were used as monomers and the fluidity modifying and waterrepellent agents were not used.

P7 was melted at 200° C. by using a screw extruder, spun through anorifice of 195° C. with 0.2 mm diameter holes and cooled in air,followed by oiling and winding at a speed of 800 m/min to give anun-drawn yarn UY7. UY7 was then drawn at a drawing temperature of 70° C.in the drawing ratio of 4.1, and heat-treated at 120° C. under tensionto give a drawn yarn DY7 of 150 d/48 f. DY7 had a strength of 4.1 g/d,an elongation of 32.0%, an initial elastic modulus (Young's modulus) of63.6 g/d, an average molecular weight of 108000, and a melting point of173° C.

The drawn yarn DY8 obtained from P8 by spinning and drawing in the samemanner as in DY7 had physical properties; strength 3.1 g/d, elongation43.1%, initial elastic modulus 36.6 g/d, average molecular weight87,000, and melting point 151° C.

P7 and P8 were melted respectively with separate screw extruders, andspun through an orifice of 195° C. with 0.2 mm diameter holes toconjugate into a concentric core-sheath type structure with P7 as thesheath and P8 as the core in the P7/P8 volume ratio of 1/1. Then thespinning and drawing were conducted in the same manner as in DY7 to givea drawn yarn DY9. DY9 had physical properties: strength 3.6 g/d,elongation 40.1%, initial elastic modulus 57.4 g/d, and averagemolecular weight 96,000.

A drawn yarn DY10 was obtained by conducting the bi-component fiberspinning and the drawing in nearly the same manner as in DY9 except thatthe P7/P8 conjugation ratio (volume) was 1/2 . The DY10 had physicalproperties: strength 3.5 g/d, elongation 31%, initial elastic modulus 51g/d, and average molecular weight 92,000.

The deterioration test was carried out by embedding DY7, DY8, DY9 andDY10 in the soil for two years. The strength retention after eachembedded period of time of each yarn is shown in Table 10.

                  TABLE 10                                                        ______________________________________                                        Months                                                                        embed- Comparative                                                                              Comparative                                                 ded    Reference  Reference  Reference                                                                             Reference                                (month)                                                                              Example 6  Example 7  Example 14                                                                            Example 15                               ______________________________________                                         0     100        100        100     100                                       1     95.3       86.3       95.5    96.0                                      2     95.0       71.0       93.7    94.8                                      3     91.1       59.6       92.0    92.2                                      4     88.7       38.1       85.6    86.4                                      5     83.5       20.2       85.2    84.3                                      6     79.2       11.5       80.3    81.5                                      8     75.0       0          73.8    70.0                                     10     69.3                  66.5    42.2                                     12     61.7                  60.2    18.4                                     14     55.6                  45.4    8.7                                      16     48.0                  28.9    0.0                                      18     43.0                  9.9                                              20     38.7                  5.2                                              22     32.5                  0.0                                              24     30.1                                                                   ______________________________________                                        Note   Single-    Single-    Bi-     Bi-                                             component  component  component                                                                             component                                       fiber      fiber      conjugate                                                                             conjugate                                       DY7        DY8        fiber   fiber                                                                 DY9     DY10                                 

As shown in Table 10, the estimated half-life of DY7 comprising aslightly degradable polyester was about 15 months, and the half-life ofDY8 comprising an easily degradable polyester was about three months. Onthe other hand, the deterioration of DY9 composed of the both polymersformed in the sheath/core ratio of 1/1 proceeded rapidly after a lapseof 12 months, and the half-life thereof was 14 months. As regards DY10formed in the sheath/core ratio of 1/2, the deterioration thereofproceeded rapidly after a lapse of eight months, and the half-lifethereof was about nine months. DY7 and DY8 each comprising a singlecomponent deteriorate nearly linearly, but each of the conjugate fibersof the present invention has the feature that the deterioration proceedsslowly during the specified period of time, and after a lapse of such aperiod, proceeds rapidly. The fibers prepared by mixing P7 with P8 andthen spinning show, in many cases, a linear deterioration characteristicthough the characteristic varies depending on the mixing condition, anddoes not show such a peculiar deterioration behavior as in the conjugatefibers of the present invention.

EXAMPLE 9

Dimethyl terephthalate and butandiol were reacted in the molar ratio of1/2.2 for trans-esterification with stirring at 180° C. for about twohours, using 200 ppm of sodium acetate as the trans-esterificationcatalyst. The resultant was then mixed with 20% of polyhexane adipatehaving a weight average molecular weight of 600 and 250 ppm of antimonytrioxide as the polymerization catalyst based on the butyleneterephthalate component. With agitating at 240° C. for one hour, thepressure was gradually decreased from 600 Torr up to 0.5 Torr, and thepolymerization was further carried out at 0.5 Torr for about four hoursto give a polybutylene terephthalate (PBT)/polyhexane adipate (PHA)copolymer P9. The P9 was mainly a block copolymer of PBT/PHA, but a partthereof was in the state of random copolymer owing to thetrans-esterification reaction.

A polylactic acid/PEG block copolymer P10 was obtained in nearly thesame manner as in the polymerization with a lactide in Reference Example14 except that 2.5% of polyethylene glycol (PEG) having a number averagemolecular weight of 6,300 was mixed to the polymerization system andreacted.

P9 was spun and drawn in the same manner as in DY7 in ComparativeReference Example 6, to give a drawn yarn DY11. The DY11 had physicalproperties: strength 3.6 g/d, elongation 58.0%, initial elastic modulus28.6 g/d, fineness 3 d, weight average molecular weight 46,000, andmelting point 231° C.

Similarly P10 was spun and drawn in the same manner to give a drawn yarnDY12. DY12 had physical properties: strength 4.3 g/d, elongation 33.1%,initial elastic modulus 59.4 g/d, fineness 3 d, average molecular weight97,000, and melting point 171° C.

P9 as the sheath component and P10 as the core component were melted bya screw extruder in the same manner as in DY9 of Reference Example 14,and formed into the concentric composite core-sheath type in the P9/P10ratio of 1/2 to give a drawn yarn DY13. DY13 had physical properties:strength 4.1 g/d, elongation 36.1%, initial elastic modulus 58.0 g/d,and the fineness 3 d.

DY11, DY12 and DY13 were embedded in soils for three years to carry outa deterioration test. As a result, the half-life of DY11 was about threeyears. The half-life of DY12 was about six months and the deteriorationthereof proceeded nearly linearly. On the other hand, the deteriorationof the conjugate fiber DY13 proceeded slowly until 24 months and afterthat rapidly advanced. The half-life was 27 months.

EXAMPLE 10

A copolymer of L-lactide and 2.5% of PEG having a number averagemolecular weight of 8,200 (easily degradable polymer 1) having a meltingpoint of 166° C. and an average molecular weight of 180,000, and a PBT(aromatic component 67%, melting point (220° C.)) having a numberaverage molecular weight of 19,000, were melt-spun at 235° C. in abi-component fiber spinning manner, followed by cooling in air, oiling,winding at a speed of 1,200 m/min, drawing 3.94 times at 80° C., andthen heat-treating at 130° C. under tension, to give a drawn yarn Y1 of150 d/48 f. The transverse sectional structure of Y1 was of radial typeas shown in FIG. 14, and the ratio (easily degradable polymer 1/aromaticpolyester) was 1/5.

A circular knitted fabric knitted with Y1 was boiled in a 0.1% aqueoussodium hydroxide solution for 15 minutes, and then washed with water anddried, to give a knitted fabric K1. The easily degradable polymer 1 inY1 was completely degraded and removed by this alkali treatment, thusthe fiber became ultrafine. K1 was very soft, and had a very excellentcleaning power to wipe off a stain on the surface of a mirror, glass andthe like. The rate of degradation (decrease in weight) of the easilydegradable polymer 1 at 25° C. in a 0.1% aqueous sodium hydroxidesolution was 10%/10 min. On the other hand, no degradation was observedon the PBT under the same conditions. The rate of degradation of thisaromatic polyester was not more than 1/200 of that of the easilydegradable polymer 1.

The cleaning power was measured by a method (method disclosed inJapanese Patent Publication Kokai No. 2-240566 by the present inventors)wherein a grease was uniformly applied onto a specular surface of achrome plated metal in an mount of 1 mg/cm², wiped off once with a knitfabric, and the residual grease on the specular surface was measured bythe reflection method, using a Fourier transform infraredspectrophotometer. The amount of the residual grease after wiping withK1 was 0.3 μg/cm², whereas the amount after wiping with a fabric beforethe alkali treatment was 33 μg/cm². That is to say, the cleaning powerof K1 was increased by about 110 times by the alkali treatment(division, forming into ultrafine fiber).

EXAMPLE 11

A polylactic acid copolymer (easily degradable polymer 2) having anaverage molecular weight of 180,000 and a melting point of 161° C. whichwas prepared by copolymerizing a mixture of L-lactide and DL-lactide inan L-lactic acid/D-lactic acid ratio of 97/3 with 2% of polyethyleneglycol having a number average molecular weight of 8,200 based on thelactic acid component, and an aromatic polyester prepared bycopolymerizing PBT with 15 % of polybutylene adipate and having a weightaverage molecular weight of 22,000, a melting point of 194° C. and anaromatic component content of 57% were spun, drawn and heat-treated inthe same manner as in Y1 of Example 10, to give a drawn yarn Y2.

A knit fabric made of Y2 was boiled in an aqueous sodium carbonatesolution (3%) for 15 minutes, followed by washing with water and dryingto give a knit fabric K2. By this weak alkali treatment, the easilydegradable polymer 2 in Y2 was completely degraded and removed, so thefiber became ultrafine. K2 was very soft and excellent in cleaningpower, like K1 of Example 10.

Conventional conjugate fibers could not be divided with weak alkalissuch as sodium carbonate. The rate of degradation of the easilydegradable polymer 2 at 25° C. in a 0.1% aqueous sodium hydroxidesolution was 15%/10 min., whereas that of the PBT/polybutylene adipatecopolymer under the same conditions was 0.1%/10 min. That is to say, thehydrolysis rate of the aromatic polyester constituting Y2 was 1/150 ofthe easily degradable polymer 2.

EXAMPLE 12 AND COMPARATIVE EXAMPLE 4

L-lactide having the optical purity of 99.7% and sufficiently dried(water content not more than 90 ppm) and pre-melted and the similarlydried and melted PEG (#6000 made by Nippon Oil & Fats Co., Ltd.) havingthe number average molecular weight of 8,200, to which 0.1% of Irganox1010 made by Ciba Geigy Corp., i.e. a hindered phenol antioxidant wasadded, were supplied to the raw material feed part of a twin-screwkneader in the ratio of 98/2. Simultaneously tin dioctylate was added asthe polymerization catalyst in an amount of 0.3% based on the lactide.The twin-screw kneader was one shown in FIGS. 1 and 2 and comprisedplural 30 mm diameter feed screws and plural 7 mm thick two blade-shapedagitating elements.

The feed screws were disposed in the raw material feed part and two venthole parts, and the agitating elements, in the other parts. The sectionof the cylinder was elliptic and constricted around the center portion,and its temperature was set at 190° C. A nitrogen gas was suppliedthrough the first vent hole and exhausted through the second vent hole.The two rotation shafts rotated in the same direction, and the number ofrotations was 60/min.

The polymer discharged from the twin-screw kneader was supplied to the25 mm diameter second twin-screw kneader directly connected thereto andhaving two vent holes. The cylinder temperature was set at 190° C. Therotation was in the same direction, and the number of rotations was40/min. A small amount of nitrogen gas was supplied through the firstvent hole, and the second vent hole was connected to the vacuum pump.The vacuum degree was kept at about 0.5 Torr, and the above-mentionedantioxidant was added in an amount of 0.1% based on the polymer. Theaverage residence (reaction) time in the first twin-screw kneader was5.5 minutes, and the residence time in the second twin-screw kneader was12 minutes. The total average polymerization time was 17.5 minutes.

The polymer discharged from the second twin-screw kneader waspressure-sent with a gear pump, and filtered through a 20 μm filter, andthen sent to the spinning head kept at 190° C. The spinning head wasprovided with two spinnerets each having 24 small holes of 0.25 mm indiameter. The spinning condition was good, and the filamentssufficiently cooled and solidified were wound as the un-drawn yarn at arate of 1,000 m/min. The average molecular weight of the copolymerentering the spinning head was 90,000.

Drawing was carried out at a drawing temperature of 70° C. in a drawingratio of 3.8, and heat-treatment after the drawing was continuouslycarried out at 120° C. The drawing was conducted satisfactorily withoutyarn breaking, thus giving a very good fiber having a strength of 4.2g/d, an elongation of 33.2%, a fiber melting point of 173° C. and a heatof fusion of 10.8 cal/g.

EXAMPLE 13

Lactide was copolymerized with PEG having a variety of number averagemolecular weights in various copolymerization proportions based on thelactide in nearly the same manner as in Example 12, and directly spunimmediately after the polymerization. The spinning and drawing wereconducted under the same conditions as in Example 10.

The physical properties of the obtained fiber are shown in Table 11.

                                      TABLE 11                                    __________________________________________________________________________    PEG                                                                           Number        Physical properties of fiber                                       average    Average          Melting                                                                            Heat of                                                                           Degree of                                molecular                                                                           Addition                                                                           molecular                                                                           Strength                                                                           Elongation                                                                          point                                                                              fusion                                                                            orientation                           No.                                                                              weight                                                                              percent                                                                            weight                                                                              (g/d)                                                                              (%)   (°C.)                                                                       (cal/g)                                                                           (%)                                   __________________________________________________________________________    1  1000  1.5  76000 3.8  36    173  10.3                                      2  2000  1.5  82000 4.1  34    174  10.7                                      3  3500  2.5  88000 4.3  32    174  11.3                                                                              85                                    4  6000  2.5  95000 4.8  36    173  10.4                                                                              87                                    5  6000  4.0  91000 4.7  35    173   9.8                                      6  8200  2.5  107000                                                                              5.5  36    172  10.3                                                                              92                                    7  8200  6.0  97000 5.1  34    173   9.5                                      8  12000 4.0  96000 4.7  32    174  11.2                                      __________________________________________________________________________

EXAMPLE 14 AND COMPARATIVE EXAMPLE 5

PEG (#6000 made by Nippon Oil & Fats Co., Ltd.) having a number averagemolecular weight of 8,200 was added in an amount of 2% based on alactide sufficiently dried (water content not more than 100 ppm) andpre-melted and having an optical purity of 99.8%, and then supplied tothe raw material feed part of a twin-screw kneader. At the same time,0.3% of tin dioctylate was added as the polymerization catalyst based onthe lactide. Polymerization was carried out by the twin-screw kneadercomprising plural 30 mm diameter feed screws and plural 7 mm thick twoblade-shaped agitating elements. The polymerization temperature was 190°C. A nitrogen gas was supplied through the first vent hole and exhaustedthrough the second vent hole. Two rotation shafts rotated in the samedirection, and the number of rotations was 60/min.

The polymer discharged from the twin-screw kneader was sent to a 40 mmdiameter second twin-screw kneader directly connected thereto and havingtwo vent holes. The cylinder temperature was 190° C. The rotation was inthe same direction, and the number of rotations was 40/min. A nitrogengas was supplied through the first vent hole, and the second vent holewas connected to the vacuum pump to keep the vacuum degree at abut. 0.5Torr, while the above-mentioned melted antioxidant was added in anamount of 0.1% based on the polymer. The polymer discharged from thesecond twin-screw kneader was pressure-sent by a gear pump, filteredwith a 20 μm filter and extruded through a 3 mm diameter nozzle,followed by cooling with water to solidify and cutting to give the chipsP11. The average residence (reaction) time of the polymer in the firsttwin-screw kneader was 5.5 minutes, and the residence time in the secondtwin-screw kneader was 16 minutes. The total average polymerization timewas 21.5 minutes. There was no discoloration on the P11 and thetransparency was excellent.

P11 was melted by a 210° C. screw extruder, spun through an orifice of200° C. having 0.2 mm diameter holes, and cooled in air, followed byoiling and winding at a speed of 800 m/min to give an un-drawn yarn UY8.UY8 was drawn at 70° C. in a drawing ratio of 3.7, and heat-treated at120° C. under tension, followed by winding at a speed of 600 m/min togive a drawn yarn DY14 of 75d/18f. Similarly a drawn yarn DY15 of 15d/4fwas obtained.

A crimping processed yarn was prepared by applying DY14 to a disc typefalse-twisting machine. The overfeed ratio was 2% and the false-twistingtemperature was 130° C., thus a good processed yarn having the number oftwists of 2,700/m was obtained. In the same manner, two yarns each of Stwist yarn and Z twist yarn were prepared.

An ester type urethane yarn of 15d/1f was elongated 4.0 times, and DY15was covered thereon at a rate of 1,900 turns/m to give a covered yarnCV1.

The covered yarn and a raw silk of 20d/6f were knitted alternately bymeans of a pantyhose knitting machine (Super 4-II made by Nagata SeikiKabushiki Kaisha having 4 ribs and 400 needles) to produce the legportion. The panty portion was also produced using a textured yarn of75d/18f.

After knitting, usual scouring was carried out at 60° C., and thepantyhose was fitted onto a foot pattern and set at 115° C. forfinishing up. The feeling of wear was somewhat harder than that of thoseusing nylon/urethane, but the feeling of touch was dry and fresh.

As a comparative example, a pantyhose using a nylon covered yarn CV2 anda finished yarn instead of the above-mentioned CV1 was produced. Whenwearing it, there was a feeling of good softness and sliminess.

EXAMPLE 15

Two kinds of pantyhoses produced in Example 14 were embedded in soil(courtyard of Gosen Kenkyusho of Kanebo, Ltd. at 4-1, Kanebo-choHofu-shi) at the end of August, and dug out of there every one month toobserve changes in appearance and strength.

The results are shown in Table 12. The pantyhose using the lactic acidfiber decreased in strength with the lapse of time, but the pantyhoseusing a nylon yarn showed almost no change.

                                      TABLE 12                                    __________________________________________________________________________    1 month later   3 months later                                                                             6 months later                                   Sample                                                                            Appearance                                                                           Strength                                                                           Appearance                                                                            Strength                                                                           Appearance                                                                           Strength                                  __________________________________________________________________________    CV1 No change                                                                            3.4 g/d                                                                            a few wrinkles                                                                        2.5 g/d                                                                            Cracks 1.5 g/d                                   CV2 No change                                                                            5.6 g/d                                                                            No change                                                                             5.5 g/d                                                                            No change                                                                            5.3 g/d                                   __________________________________________________________________________

The biodegradable copolyesters of the present invention are excellent inbiodegradability, toughness heat resistance, transparency andmelt-fluidity, and allow to conduct melt-polymerization, melt-forming,melt-filming (film formation) and melt-spinning smoothly and highefficiently. Also the copolyesters of the present invention assure lessdeterioration and discoloration, and are excellent in uniformity andtransparency, thus high quality molded articles, films, fibers and thelike can be produced in high efficiency. In conventional methods, due todeteriorated matters and modified matters produced in the polymerizationstep, there generated many so-called fish eyes and mottles on theobtained products, which not only impaired the appearance but also madeit impossible to conduct smooth and highly efficient production of filmsand fibers. The copolyesters of the present invention have made itpossible for the first time to provide polymers enabling industrialproduction of films and fibers.

Also the copolyesters of the present invention, as compared withun-modified polylactic acid, have features such as 1 a high rate ofdegradation, 2 an excellent impact resistance and 3 an excellent dyeingproperty, and are widely applicable to fibers, films and moldedarticles. High rate of degradation is suitable for uses, for example,packaging films and other disposable articles which require earlydegradation. Excellent impact resistance is suitable for use in variousmolded articles, and excellent dyeing property is suitable for use infibers for clothing and non-clothing uses.

Among the molded articles of the present invention, heat-adhesivepolylactic acid fibers comprise conjugate fibers of polylacticacid-based polymers having different melting points and, therefore, onlyone polymer portion can be melted, by heating and pressing at a giventemperature, to fuse the fibers together with maintaining the shape offibers. For this reason, the use of the heat-adhesive polylactic acidfiber of the present invention can make it possible to manufacture atotally complete circulation type biodegradable non-woven fabric withouta binder.

Also, when the filament yarns (heat-adhesive polylactic acid fiber)which are a molded article of the present invention, are laid crosswiseat a right angle or formed into a low density woven fabric or a plaingauze and the crossing points of the yarns are melted to fuse together,an extra light weight net can be obtained as a novel completelybiodegradable packaging materials. Further an air-tight cloth can beobtained by passing a knitted cloth or woven cloth through heat calenderrolls to fuse surface of them.

The conjugate fibers among the molded articles of the present inventioncan offer a very preferable characteristic, with a high reliability,such that the deterioration of strength thereof is slow during use (alsoprior to use) and advances rapidly after the service life. In contrast,conventional single component type degradable fibers have a seriousproblem that since the deterioration thereof advances nearly linearlywith the lapse of time, the advance of deterioration is remarkable evenduring use and therefore the service life (usable period) is not clear.Also, the deterioration advances after the service life at nearly thesame speed as in use, and therefore in case of articles having a longlife, matters remaining without deteriorating may cause varioustroubles. The conjugate fibers of the present invention can be rapidlydeteriorated after used, such troubles can be prevented. Further theconjugate fibers of the present invention have a very great feature thatthe fibers having a wide range of degradation characteristics can befreely designed and manufactured easily in high efficiency by selectingpolymers for sheath and core components, the ratio of the components andthe sectional shape thereof. Also in the conjugate fibers of the presentinvention, the sheath portion is sufficiently drawn, and sufficientlystrong adhesion between the sheath and the core can be achieved, andaccordingly it is possible to prevent the sheath from being easilydamaged even by an external force such as friction and from beingseparated from the core. This feature can be fully exhibited even inpractical use, thus giving a fairly high reliability.

As to the conjugate fibers among the molded articles of the presentinvention, those excellent in uniformity can be produced at a highspeed, thus very advantageous industrially as compared with onesproduced by a conventional coating method or the like.

In the conjugate fibers among the molded articles of the presentinvention, an easily degradable polymer is degraded and removed inneutral environment, in weak alkali environment and by an action oforganisms, so there can be obtained safely, easily and high efficientlyfine fibers, ultrafine fibers, modified cross-section fibers and specialsection fibers. For degradation treatment and neutralization of wastewater, a small amount of chemicals suffices, and organic matters inwaste water can be easily and completely removed by an activated sludgeprocess. Thus the above-mentioned conjugate fibers are very desirablefrom the viewpoint of environmental protection. Also they have thefeature that they are divided even in the sea and soil. In that case, nospecial dividing step is necessary and they are expected to be appliedto new uses utilizing this feature, for example, development of novelproducts for agricultural and fishery uses, and to novel suture.

By the process of the present invention, the number of steps isremarkably decreased as compared with conventional processes, thusbiodegradable polyester fibers excellent in strength and/or heatresistance can be obtained inexpensively. In particular, a significantlyepock-making effect that the molecular weight of polylactic acidpolymers is hardly decreased, can be achieved by directly connecting thepolymerization step and the spinning step.

INDUSTRIAL APPLICABILITY

The biodegradable copolyesters of the present invention have abiodegradability, is excellent in toughness and heat resistance, andalso is less susceptible to deterioration and discoloration andexcellent in uniformity, transparency and melt-fluidity. Further, themelt-polymerization can be conducted smoothly and high efficiently, andin addition, the melt-forming, melt-film formation and melt-spinning canbe carried out smoothly in high efficiency. Therefore, the copolyestersare used for manufacturing molded articles, films, fibers and the like.

Also various molded articles manufactured by using the biodegradablecopolyesters of the present invention having characteristics asmentioned above are suitably used in a wide range of uses and fields,for instance, general packaging and food packaging materials andagricultural materials or the like in case of films, clothing,non-clothing, medical and sanitary materials, agricultural materials,fishing lines, fishing nets, materials for general use, industrialmaterials or the like in case of fibers, and also in the form of knittedarticles, woven articles, non-woven fabrics, paper, felts, yarns, cords,ropes and other forms.

Also the molded articles of the present invention are applicable to, forexample, containers for foods and drinks, detergents and other dailynecessaries, chemicals, cosmetics, and the like, parts of machines andelectronic devices, furnitures, building materials, and other uses, andalso can be widely used in the fields to which conventional polylacticacid homopolymer has not been applicable because of brittleness. Whileconventional polylactic acid/PEG copolymers are poor in strength andheat resistance, the molded articles of the present invention haveexcellent toughness and heat resistance, which enable sterilization byboiling or high pressure steam, and therefore can also be suitably usedin the fields of medical, sanitary materials, foods, cosmetics and thelike.

Among the molded articles of the present invention, heat-adhesivepolylactic acid fibers comprise conjugate fibers of polylacticacid-based polymers having different melting points and, therefore, onlyone polymer portion can be melted, by heating and pressing at a giventemperature, to fuse the fibers together with maintaining the shape offibers. For this reason, the use of the heat-adhesive polyactic acidfiber of the present invention can make it possible to manufacture atotally complete circulation type biodegradable non-woven fabric withouta binder. The obtained non-woven fabric has sufficient tensile strength,tearing resistance and peel strength and, therefore, is suitable foruses such as bags for civil engineering and construction, vegetationmats and the like, and is also suitable as clothes and sanitary goods.The fabric is of high utility value as completely biodegradablematerials which have not been hitherto obtained, and is particularlyuseful as a wound covering material having biocompatibility.

Also, when the filament yarns which are a molded article of the presentinvention, are laid crosswise at a right angle or formed into a lowdensity woven fabric or a plain gauze and the crossing points of theyarns are melted to fuse together, an extra light weight net can beobtained as a novel completely biodegradable packaging materials.Further an air-tight cloth can be obtained by passing a knitted wovencloth through heat calender rolls to fuse surface of them.

The fibers which are the molded articles in the present invention may beused for obtaining continuous filament, cut staple, and various fibersby Spun-Bond method, flush spinning method and the like.

In the usual clothing field too, the fibers of the present invention canbe used for inner wears and stockings to which no application has beenmade, because the Young's modulus and elastic recovery were on the samelevel as nylon.

We claim:
 1. A biodegradable copolyester comprising an L-lactic acidand/or D-lactic acid component as a main component and having a weightaverage molecular weight of at least 50,000, produced by copolymerizingsaid lactic acid component with at least one member of (A) 0.1 to 15% byweight of a polyethylene glycol having a number average molecular weightof at least 300, (B) an aliphatic polyester and (C) a sulfogroup-containing aromatic compound having two ester-forming groups. 2.The biodegradable copolyester of claim 1, wherein the biodegradablecopolyester comprising the L-lactic acid and/or D-lactic acid componentas a main component produced by copolymerizing with the polyethyleneglycol having a number average molecular weight of at least 300 is oneproduced by copolymerizing 99.9 to 85% by weight of the L-lactic acidand/or D-lactic acid component and 0.1 to 15% by weight of thepolyethylene glycol having a number average molecular weight of at least300, and the melting point is not less than 110° C.
 3. The biodegradablecopolyester of claim 1, wherein the biodegradable copolyester comprisingthe L-lactic acid and/or D-lactic acid component as a main componentproduced by copolymerizing with the aliphatic polyester is one producedby copolymerizing 99.5 to 85% by weight of the L-lactic acid and/orD-lactic acid component and 0.5 to 15% by weight of the aliphaticpolyester, and the weight average molecular weight is not less than80,000 and the melting point is not less than 110° C.
 4. Thebiodegradable copolyester of claim 1, wherein the biodegradablecopolyester comprising the L-lactic acid and/or D-lactic acid componentas a main component produced by copolymerizing with the sulfogroup-containing aromatic compound having two ester-forming groups isone produced by copolymerizing 99.5 to 80% by weight of the L-lacticacid and/or D-lactic acid component and 0.5 to 20% by weight of thesulfo group-containing aromatic compound having two ester-forminggroups.
 5. A molded article produced by melt-forming a biodegradablecopolyester comprising an L-lactic acid and/or D-lactic acid componentas a component and having a weight average molecular weight of at least50,000, said copolyester being produced by copolymerizing said lacticacid component with at least one member of (A) a polyethylene glycolhaving a number average molecular weight of at least 300, (B) analiphatic polyester and (C) a sulfo group-containing aromatic compoundhaving two ester-forming groups.
 6. The molded article of claim 5,wherein said molded article produced by melt-forming is a conjugatefiber comprising (a) a biodegradable copolyester having a melting pointTa and (b) a biodegradable copolyester which has a melting point lowerthan Ta by at least 10° C. or which is amorphous and has no meltingpoint.
 7. The molded article of claim 5, wherein said molded articleproduced by melt-forming is composed of a sheath made of a lessdegradable copolyester that the rate of degradation by biodegradation orby hydrolysis in neutral water or aqueous solution is low, and a coremade of a biodegradable copolyester having a rate of degradation of atleast 2 times the rate of degradation of said sheath, and both said coreand sheath components are molecular-oriented.
 8. The molded article ofclaim 5, wherein said molded article produced by melt-forming is adividable conjugate fiber made of said biodegradable copolyester and afiber-forming copolyester containing at least 40% by weight of acomponent derived from an aromatic compound, wherein said fiber-formingcopolyester is divided by said biodegradable copolyester into aplurality of segments in the transverse section of the single fiber andsaid biodegradable copolyester occupies at least a part of the fibersurface.
 9. A process for producing a molded article of a biodegradablecopolyester, which comprises subjecting a molten mixture containing atleast one lactic acid component selected from the group consisting ofL-lactic acid, D-lactic acid, L-lactide and D-lactide and at least onemember selected from the group consisting of (A) a polyethylene glycolhaving a number average molecular weight of at least 300, (B) analiphatic polyester and (C) a sulfo group-containing aromatic compoundhaving two ester-forming groups to a melt-polymerization in a continuouspolymerization manner for less than one hour to produce a biodegradablecopolyester having a weight average molecular weight of at least 50,000,introducing said copolyester directly to a molding machine withoutsolidification and pelletization thereof, and melt-forming saidcopolyester into an article.
 10. The process of claim 9, wherein saidmolten mixture contains 99.5 to 85% by weight of said lactic acidcomponent and 0.1 to 15% by weight of said polyethylene glycol (A), andsaid biodegradable copolyester has a weight average molecular weight ofat least 70,000 and is directly led to a spinning head withoutsolidification and pelletization thereof and is subjected tomelt-spinning, drawing at least three times and heat-treatment to imparta fiber strength of at least 3 g/d while maintaining said weight averagemolecular weight of at least 70,000.
 11. The biodegradable copolyesterof claim 1, wherein the content of said lactic acid component is 85 to99.5% by weight.
 12. The biodegradable copolyester of claim 1, whereinthe content of said lactic acid component is 90 to 99.9% by weight. 13.The biodegradable copolyester of claim 1, which has a weight averagemolecular weight of at least 80,000.
 14. The biodegradable copolyesterof claim 1, which has a weight average molecular weight of at least100,000.
 15. The biodegradable copolyester of claim 1 further comprisinga chain extending agent selected from the group consisting of adicarboxylic acid component and a diol component.
 16. The biodegradablecopolyester of claim 1, which is a polylactic acid/polyethylene glycolcopolymer wherein a polylactic acid segment is attached to each ofterminal hydroxyl groups of a polyethylene glycol chain through esterlinkage and lactic acid molecules in said polylactic acid segment arelinked to each other through ester linkages.
 17. The biodegradablecopolyester of claim 16, said polylactic acid/polyethylene glycolcopolymer has a weight average molecular weight of at least 60,000. 18.The biodegradable copolyester of claim 16, wherein said polylacticacid/polyethylene glycol copolymer has a melting point of not less than130° C.
 19. The biodegradable copolyester of claim 16, wherein saidpolylactic acid/polyethylene glycol copolymer has a melting point of notless than 150° C.
 20. The biodegradable copolyester of claim 16, wheresaid polyactic acid/polyethylene glycol copolymer further contains acopolymerized residue that is at least one member selected from thegroup consisting of dicarboxylic acid, a sulfo group-containing compoundand an amino or amido group-containing compound.
 21. The biodegradablecopolyester of claim 16, wherein the content of lactic acid in saidpolylactic acid/polyethylene glycol copolymer is 85 to 99.5% by weight.22. The biodegradable copolyester of claim 1, which is polylacticacid/aliphatic polyester copolymer containing 0.5 to 15% by weight ofsaid aliphatic polyester, wherein a polylactic acid segment is attachedto each of terminal groups of an aliphatic polyester chain through esterlinkage.
 23. The process of claim 9, wherein a chain extending agent isadded to said molten mixture.
 24. The process of claim 9, wherein saidlactic acid component is L-lactide, D-lactide or a mixture thereof.